drm/vc4: txp: Add support for BCM2712 MOP

The BCM2712 has an evolution of what used to be called TXP in the
earlier SoCs, but is now called MOP.

There's a few differences still, so we can add a new compatible to deal
with them easily.

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