drm/amdkfd: Clear MODE.VSKIP in gfx9 trap handler

If user shader issues S_SETVSKIP then this state will persist when
executing the trap handler, causing vector instructions to be
skipped.

VSKIP state is already saved/restored through the MODE register.

Signed-off-by: Jay Cornwall <jay.cornwall@amd.com>
Reviewed-by: Lancelot Six <lancelot.six@amd.com>
Suggested-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

Author: jcornwallAMD