drm/amdkfd: To fix sdma page fault issue for GC 11

For the MQD memory, KMD would always allocate 4K memory,
and mes scheduler would write to the end of MQD for unmap flag.

Signed-off-by: Ruili Ji <ruiliji2@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>