drm/nouveau/kms/nvd9-: Fix disabling CRCs alongside OR reprogramming

While I had thought I'd tested this before, it looks like this one issue
slipped by my original CRC patches. Basically, there seem to be a few
rules we need to follow when sending CRC commands to the display
controller:

* CRCs cannot be both disabled and enabled for a single head in the same
  flush
* If a head with CRC reporting enabled switches from one OR to another,
  there must be a flush before the OR is re-enabled regardless of the
  final state of CRC reporting.

So, split nv50_crc_atomic_prepare_notifier_contexts() into two
functions:
* nv_crc_atomic_release_notifier_contexts() - checks whether the CRC
  notifier contexts were released successfully after the first flush
* nv_crc_atomic_init_notifier_contexts() - prepares any CRC notifier
  contexts for use before enabling reporting

Additionally, in order to force a flush when we re-assign ORs with heads
that have CRCs enabled we split our atomic check function into two:

* nv50_crc_atomic_check_head() - called from our heads' atomic checks,
  determines whether a state needs to set or clear CRC reporting
* nv50_crc_atomic_check_outp() - called at the end of the atomic check
  after all ORs have been added to the atomic state, and sets
  nv50_atom->flush_disable if needed

Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Ben Skeggs <skeggsb@gmail.com>
Acked-by: Dave Airlie <airlied@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200629223635.103804-1-lyude@redhat.com