[AArch64] Don't rename registers with pseudo defs in Ld/St opt.

If the root def of for renaming is a noop-pseudo instruction like kill,
we would end up without a correct def for the renamed register, causing
miscompiles.

This patch conservatively bails out on any pseudo instruction.

This fixes https://bugs.chromium.org/p/chromium/issues/detail?id=1037912#c70