Merge, from trunk, r2979

Merge, from trunk, r2979
* add a missing extra m-reg check for some LD/ST vector cases

* implement
  LD1/ST1 (multiple 1-elem structs to/from 2 regs
  LD1/ST1 (multiple 1-elem structs to/from 3 regs
  LD1/ST1 (multiple 1-elem structs to/from 4 regs
  LD1R (single structure, replicate)
  LD2R (single structure, replicate)
  LD3R (single structure, replicate)
  LD4R (single structure, replicate)
  LD1/ST1 (single structure, to/from one lane)
  LD2/ST2 (single structure, to/from one lane)
  LD3/ST3 (single structure, to/from one lane)
  LD4/ST4 (single structure, to/from one lane)

I believe this completes the implementation of load and store
instructions for AArch64 ARMv8.

git-svn-id: svn://svn.valgrind.org/vex/branches/VEX_3_10_BRANCH@3006