Revert "[PPC64] Fix DQ-form instruction handling and emit error for misalign..."

This reverts commit 5125b44dbb5d06b715213e4bec75c7346bfcc7d3.
ppc64-dq.s and ppc64-error-missaligned-dq.s fail on several of the build-bots.
Reverting to investigate.

llvm-svn: 340568