Merge changes I3d950e72,Id315a8fe,Ib62e6e9b,I1d0475b2 into integration

* changes:
  perf(cm): drop ZCR_EL3 saving and some ISBs and replace them with root context
  perf(psci): get PMF timestamps with no cache flushes if possible
  perf(amu): greatly simplify AMU context management
  perf(mpmm): greatly simplify MPMM enablement