[X86] Rename BNDMOV instructions and hide redundant instruction encoding from the assembler.

Favor the 0x1a encoding for register/register move to match gas.

The instructions used RM and MR in their name along with rr/rm/mr at the end. To make more consistent with other instructions remove the RM/MR and use rr/rm/mr/rr_REV.

Hide the _REV encoding from the assembler but leave it for the disassembler.

llvm-svn: 331101