drm/vc4: dpi: Support BGR666 formats

The VC4 DPI output can support multiple BGR666 variants, but they were
never added to the driver. Let's add the the support for those formats.

Signed-off-by: Joerg Quinten <aBUGSworstnightmare@gmail.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Link: https://lore.kernel.org/r/20221013-rpi-dpi-improvements-v3-5-eb76e26a772d@cerno.tech


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