drm/vc4: dpi: Add support for composite syncs to vc4_dpi

The hardware can combine H&V syncs onto the output enable line
as composite syncs, so add the relevant configuration to do that.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Link: https://lore.kernel.org/r/20220613144800.326124-9-maxime@cerno.tech


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