drm/vc4: dpi: Support RGB565 format

The RGB565 format with padding over 24 bits
(MEDIA_BUS_FMT_RGB565_1X24_CPADHI) is supported by the vc4 DPI
controller. This is what the Geekworm MZP280 DPI display uses, so let's
add support for it in the DPI controller driver.

Reviewed-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Signed-off-by: Chris Morgan <macromorgan@hotmail.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Link: https://lore.kernel.org/r/20221013-rpi-dpi-improvements-v3-4-eb76e26a772d@cerno.tech


Signed-off-by: Maxime Ripard <maxime@cerno.tech>