drm/vc4: hdmi: Raise the maximum clock rate

Now that we have the infrastructure in place, we can raise the maximum
pixel rate we can reach for HDMI0 on the BCM2711.

HDMI1 is left untouched since its pixelvalve has a smaller FIFO and
would need a clock faster than what we can provide to support the same
modes.

Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>