[AMDGPU] Move WQM Pass after MI Scheduler

[AMDGPU] Move WQM Pass after MI Scheduler

Exec mask manipulation inserted by SIWholeQuadMode barriers to
instruction scheduling.  Move the entire pass after the machine
instruction scheduler and make changes so pass is correct for
non-SSA operation.  These changes should leave the pass still
usable pre-scheduler, although tests have be updated to reflect
post-scheduler results.

Reviewed By: nhaehnle

Differential Revision: https://reviews.llvm.org/D88081