allow option to enforce mirroring of all system memory

nest_attributes.xml:
  add REQUESTED enum to ATTR_MRW_HW_MIRRORING_ENABLE, takes prior behavior of
  TRUE enum
  new TRUE enum behavior enforces that all memory will be mirrored

p9_mss_eff_grouping:
  prohibit group formation of size 1, 2 (cross-MCS), or 3
  if ATTR_MRW_HW_MIRRORING_ENABLE is TRUE -- this will
  ensure that all groups formed support mirroring

  commit log for each DIMM which is ungrouped

p9_mss_setup_bars, p9_query_mssinfo, p9_setup_bars:
  Minor changes to adapt to new enum definition

Change-Id: I328b7b063bf79d534b1b466560309c0ccae5a4f5
CQ: SW436871
Reviewed-on: http://ralgit01.raleigh.ibm.com/gerrit1/61483
Tested-by: Jenkins Server <pfd-jenkins+hostboot@us.ibm.com>
Tested-by: HWSV CI <hwsv-ci+hostboot@us.ibm.com>
Tested-by: PPE CI <ppe-ci+hostboot@us.ibm.com>
Tested-by: Hostboot CI <hostboot-ci+hostboot@us.ibm.com>
Reviewed-by: William G. Hoffa <wghoffa@us.ibm.com>
Reviewed-by: Nicholas E. Bofferding <bofferdn@us.ibm.com>
Reviewed-by: Ravi Medikonduru <ravimed1@us.ibm.com>
Reviewed-on: http://ralgit01.raleigh.ibm.com/gerrit1/61499
Tested-by: Jenkins OP Build CI <op-jenkins+hostboot@us.ibm.com>
Tested-by: Jenkins OP HW <op-hw-jenkins+hostboot@us.ibm.com>
Tested-by: FSP CI Jenkins <fsp-CI-jenkins+hostboot@us.ibm.com>