add RAA229618 VIN monitoring

[bcantrill]

Draft commit comment:

In our ongoing attempts to characterize sags in the V12_SYS_A2 rail,
we enlist one of the RAA229618 VRs to record observed READ_VIN values
whenever the rail drops below 11.75V.

Example output:

 NDX LINE      GEN    COUNT PAYLOAD
   0   99        1        1 Initializing
   1  103        1        1 LimitLoaded
   2  107        1        1 FaultsCleared
   3  116        1        1 Initialized
   4  124        1        1 Notified
   5  127        1        1 Fault
   6  144        1        1 Reading { timestamp: 0x271cb, volts: Volts(11.680001) }
   7  144        1        1 Reading { timestamp: 0x271cc, volts: Volts(11.610001) }
   8  144        1        1 Reading { timestamp: 0x271cd, volts: Volts(11.500001) }
   9  144        1        1 Reading { timestamp: 0x271ce, volts: Volts(11.440001) }
  10  144        1        1 Reading { timestamp: 0x271cf, volts: Volts(11.380001) }
  11  144        1        1 Reading { timestamp: 0x271d0, volts: Volts(11.280001) }
  12  144        1        1 Reading { timestamp: 0x271d0, volts: Volts(11.190001) }
  13  144        1        1 Reading { timestamp: 0x271d1, volts: Volts(11.1) }
  14  144        1        1 Reading { timestamp: 0x271d2, volts: Volts(11.010001) }
  15  144        1        1 Reading { timestamp: 0x271d3, volts: Volts(10.960001) }
  16  144        1        1 Reading { timestamp: 0x271d4, volts: Volts(10.860001) }
  17  144        1        1 Reading { timestamp: 0x271d5, volts: Volts(10.77) }
  18  144        1        1 Reading { timestamp: 0x271d6, volts: Volts(10.68) }
  19  144        1        1 Reading { timestamp: 0x271d7, volts: Volts(10.610001) }
  20  144        1        1 Reading { timestamp: 0x271d7, volts: Volts(10.52) }
  21  144        1        1 Reading { timestamp: 0x271d8, volts: Volts(10.460001) }
  22  144        1        1 Reading { timestamp: 0x271d9, volts: Volts(10.35) }
  23  144        1        1 Reading { timestamp: 0x271da, volts: Volts(10.280001) }
  24  144        1        1 Reading { timestamp: 0x271db, volts: Volts(10.22) }
  25  144        1        1 Reading { timestamp: 0x271dc, volts: Volts(10.1) }
  26  144        1        1 Reading { timestamp: 0x271dd, volts: Volts(10.040001) }
  27  144        1        1 Reading { timestamp: 0x271de, volts: Volts(9.940001) }
  28  144        1        1 Reading { timestamp: 0x271df, volts: Volts(9.870001) }
  29  144        1        1 Reading { timestamp: 0x271df, volts: Volts(9.790001) }
  30  144        1        1 Reading { timestamp: 0x271e0, volts: Volts(9.710001) }
  31  144        1        1 Reading { timestamp: 0x271e1, volts: Volts(9.620001) }
  32  144        1        1 Reading { timestamp: 0x271e2, volts: Volts(9.530001) }
  33  144        1        1 Reading { timestamp: 0x271e3, volts: Volts(9.460001) }
  34  144        1        1 Reading { timestamp: 0x271e4, volts: Volts(9.370001) }
  35  144        1        1 Reading { timestamp: 0x271e5, volts: Volts(9.290001) }
  36  144        1        1 Reading { timestamp: 0x271e6, volts: Volts(9.22) }
  37  144        1        1 Reading { timestamp: 0x271e6, volts: Volts(9.120001) }
  38  144        1        1 Reading { timestamp: 0x271e7, volts: Volts(9.05) }
  39  144        1        1 Reading { timestamp: 0x271e8, volts: Volts(8.97) }
  40  144        1        1 Reading { timestamp: 0x271e9, volts: Volts(8.89) }
  41  144        1        1 Reading { timestamp: 0x271ea, volts: Volts(8.81) }
  42  144        1        1 Reading { timestamp: 0x271eb, volts: Volts(8.72) }
  43  144        1        1 Reading { timestamp: 0x271ec, volts: Volts(8.650001) }
  44  144        1        1 Reading { timestamp: 0x271ed, volts: Volts(8.56) }
  45  144        1        1 Reading { timestamp: 0x271ee, volts: Volts(8.490001) }
  46  144        1        1 Reading { timestamp: 0x271ee, volts: Volts(8.400001) }
  47  144        1        1 Reading { timestamp: 0x271ef, volts: Volts(8.31) }
  48  144        1        1 Reading { timestamp: 0x271f0, volts: Volts(8.240001) }
  49  144        1        1 Reading { timestamp: 0x271f1, volts: Volts(8.150001) }
  50  144        1        1 Reading { timestamp: 0x271f2, volts: Volts(8.040001) }
  51  144        1        1 Reading { timestamp: 0x271f3, volts: Volts(7.9900007) }
  52  144        1        1 Reading { timestamp: 0x271f4, volts: Volts(7.9800005) }
  53  144        1        1 Reading { timestamp: 0x271f5, volts: Volts(7.9900007) }
  54  144        1        1 Reading { timestamp: 0x271f5, volts: Volts(7.9800005) }
  55  144        1        1 Reading { timestamp: 0x271f6, volts: Volts(7.9900007) }