ARM64: add support for cache management instructions (VEX side):
  dc cvau, regX
  ic ivau, regX
  mrs regX, ctr_el0
Fixes #333228 and #333230.



git-svn-id: svn://svn.valgrind.org/vex@2851 8f6e269a-dfd6-0310-a8e1-e2731360e62c