drm/plane: check that fb_damage is set up when used

drm/plane: check that fb_damage is set up when used

There's two stages of manual upload/invalidate displays:
- just handling dirtyfb and uploading the entire fb all the time
- looking at damage clips

In the latter case we support it through fbdev emulation (with
fb_defio), atomic property, and with the dirtfy clip rects.

Make sure at least the atomic property is set up as the main official
interface for this. Ideally we'd also check that
drm_atomic_helper_dirtyfb() is used and that fbdev defio is set up,
but that's quite a bit harder to do. Ideas very much welcome.

From a cursor audit drivers seem to be getting this right mostly, but
better to make sure. At least no one is bypassing the accessor
function.

v2:
- use drm_warn_once with a meaningful warning string (José)
- don't splat in the atomic check code for everyone (intel-gfx-ci)

Reviewed-by: José Roberto de Souza <jose.souza@intel.com> (v1)
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
Cc: José Roberto de Souza <jose.souza@intel.com>
Cc: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210723083457.696939-2-daniel.vetter@ffwll.ch