When a wavefront raises TRAPSTS.XNACK_ERROR with STATUS.ALLOW_REPLAY=0
subsequent memory instructions have undefined behavior. In practice
SQC stores continue to work but TCP stores do not.

Context save is permitted to fail after XNACK error because the
wavefront will be halted and subsequently terminated. However the
debugger has an interest in retrieving the wavefront VGPR/LDS state.

Detect the out-of-spec case and use SQC stores during context save
in place of TCP stores.
Signed-off-by: Jay Cornwall <jay.cornwall@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>