drm/amdkfd: Do not include VGPR MSBs in saved PC during save

drm/amdkfd: Do not include VGPR MSBs in saved PC during save

The current trap handler uses the top bits of ttmp1 to store a copy of
sq_wave_mode.*vgpr_msb (except for src2_vgpr_msb).  This is so the
effective values in sq_wave_mode can be cleared to ensure correct
behavior of the trap handler.

When saving sq_wave_mode, the trap handler correctly rebuilds the
expected value (with *vgpr_msb restored), so the save area is correct.
However, the PC itself is copied from ttmp[0:1], which contains the
wave's PC as well as the saved MSBs.

The debugger reads the PC from the save area and is confused when non-0
values from VGPR_MSBs are present.

This patch fixes this by saving the PC in the save area's PC slot, not
the composite of the PC and VGPR_MSBs.  On restore, the VGPR_MSBs are
restored from sq_wave_mode.

Signed-off-by: Lancelot Six <lancelot.six@amd.com>
Tested-by: Alexey Kondratiev <Alexey.Kondratiev@amd.com>
Reviewed-by: Jay Cornwall <jay.cornwall@amd.com>
Cc: Vladimir Indic <vladimir.indic@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>