drm/amdkfd: Use SQC when TCP would fail in gfx10.1 context save

Similarly to gfx9, gfx10.1 drops vector stores when an xnack error is
raised. To work around this issue, use scalar stores instead of vector
stores when trapsts.xnack_error == 1.

Signed-off-by: Laurent Morichetti <laurent.morichetti@amd.com>
Reviewed-by: Jay Cornwall <jay.cornwall@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>