drm/vc4: hvs: Fix colour order for xRGB1555 on HVS5

Same as the xRGB8888 formats, HVS5 has managed to swap the colour
channels for the xRGB1555 formats as well. Add the relevant
config for pixel_order_hvs5.

Fixes: c54619b0 ("drm/vc4: Add support for the BCM2711 HVS5")
Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Link: https://lore.kernel.org/r/20221207-rpi-hvs-crtc-misc-v1-6-1f8e0770798b@cerno.tech


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