arm: warn not fail on use of missing miscreg CNTHCTL_EL2

During host bootup, KVM reads/writes to CNTHCTL_EL2. Because this
miscreg has not been implemented, the simulation would end there. This
patch causes the simulation to warn about the read/write instead of fail.

Change-Id: If034bfd0818a9a5e50c5fe86609e945258c96fa3

src/arch/arm/miscregs.cc

@@ -1291,7 +1291,7 @@ bitset<NUM_MISCREG_INFOS> miscRegInfo[NUM_MISCREGS] = {
     // MISCREG_CNTVOFF_EL2
     bitset<NUM_MISCREG_INFOS>(string("11111100000000000001")),
     // MISCREG_CNTHCTL_EL2
-    bitset<NUM_MISCREG_INFOS>(string("01111000000000000000")),
+    bitset<NUM_MISCREG_INFOS>(string("01111000000000000100")),
     // MISCREG_CNTHP_TVAL_EL2
     bitset<NUM_MISCREG_INFOS>(string("01111000000000000000")),
     // MISCREG_CNTHP_CTL_EL2