drm/crc-debugfs: Add notes about CRC<->commit interactions

CRC generation can be impacted by commits coming from userspace, and
enabling CRC generation may itself trigger a commit. Add notes about
this to the kerneldoc.

Changes since v1:
 - Clarified that anything that would disable CRCs counts as a full
   modeset, and so userspace needs to reconfigure after full modesets

Changes since v2:
 - Add these notes
 - Rebase onto drm-misc-next (trivial conflict in comment)

Signed-off-by: Brian Starkey <brian.starkey@arm.com>
Signed-off-by: Ayan Kumar Halder <ayan.halder@arm.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

Link:- https://patchwork.freedesktop.org/patch/321974/