drm: rp1: Enable VEC->GPIO output; cosmetic change to registers

In the VEC driver, enable mapping VEC (not DPI) to DPI GPIOs.
This is to support VEC output over GPIO on Raspberry Pi 5 CM5.
It is harmless as DPI and VEC could not be used concurrently,
and the output is anyway conditional on pinctrl.

Also, tweak the style of VIDEO_OUT_CFG register definitions
(in both DPI and VEC drivers) to be more Linux-friendly.

Signed-off-by: Nick Hollinghurst <nick.hollinghurst@raspberrypi.com>

Author: njhollinghurst