drm: rcar-du: Introduce new rcar_du_crtc_atomic_modeset helper

The modeset operations need to be perfomed after we have disabled
relevant CRTCs but before we commit the newly configured planes.

Introduce a new helper rcar_du_crtc_atomic_modeset() to iterate all
CRTCs in the state transaction and perform any mode setting operations.

Signed-off-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
3 files changed