drm/vc4: crtc: Add support for BCM2712 PixelValves

The PixelValves found on the BCM2712 are similar to the ones found in
the previous generation.

Compared to BCM2711, the pixelvalves only drive one HDMI controller each
and HDMI1 PixelValve has a FIFO long enough to support 4k at 60Hz.

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