Use the same gfx_*_mqd_commit function for kfd and amdgpu codepaths.

This removes the last duplicates of this programming sequence.

v2: fix cp_hqd_pq_wptr value
Reviewed-by: Edward O'Callaghan <funfunctor@folklore1984.net>
Acked-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Andres Rodriguez <andresx7@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>