drm/amdkfd: Extend PM4 packets to support 8 SDMA

Extend map_queue and unmap_queue PM4 packets to support 8
SDMA engines. The new format is backward compatible.

Signed-off-by: Oak Zeng <Oak.Zeng@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>