drm/amd/sched: allow clients to edit an entity's rq v2

This is useful for changing an entity's priority at runtime.

v2: don't modify the order of amd_sched_entity members

Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Andres Rodriguez <andresx7@gmail.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>