In order to prevent stall from happening during the system suspend operations,
the DPU KMS driver should use a freezable and unbound work queue for nonblock
commits to make sure all work items are drained in the freeze phase of the
suspend operations.  So, let's hook up a commit function of our own onto
->atomic_commit to replace the original one drm_atomic_helper_commit() which
uses the system_unbound_wq(unfreezable).  The new function is almost a copy
of drm_atomic_helper_commit() expect for the work queue replacement.

Note that other drivers which use drm_atomic_helper_commit() may have
the same problem during system suspend.  The right fix should be at the
DRM atomic core.  However, being conservative for now, it is okay to fix the
issue for this driver only.

Signed-off-by: Liu Ying <victor.liu@nxp.com>