drm: drm_atomic_helper: Add a new helper to deal with the writeback connector validation
Add a helper function to validate the connector configuration received in
the encoder atomic_check by the drivers.
So the drivers don't need to do these common validations themselves.
V2: Move the format verification to a new helper at the drm_atomic_helper.c
(Thomas Zimmermann).
V3: Format check improvements (Leandro Ribeiro).
Minor improvements(Thomas Zimmermann).
V5: Fix some grammar issues in the commit message (André Almeida).
Reviewed-by: Melissa Wen <mwen@igalia.com>
Signed-off-by: Igor Torrente <igormtorrente@gmail.com>
Signed-off-by: Melissa Wen <melissa.srw@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220905190811.25024-4-igormtorrente@gmail.com