dt-bindings: display: vc4: pv: Add BCM2711 pixel valves

The BCM2711 comes with other pixelvalves that have different requirements
and capabilities. Let's document their compatible.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Tested-by: Chanwoo Choi <cw00.choi@samsung.com>
Tested-by: Hoegeun Kwon <hoegeun.kwon@samsung.com>
Tested-by: Stefan Wahren <stefan.wahren@i2se.com>
Reviewed-by: Rob Herring <robh+dt@kernel.org>
Reviewed-by: Eric Anholt <eric@anholt.net>
Link: https://patchwork.freedesktop.org/patch/msgid/3a21824460d96245984d730e446863a4853f2ae5.1599120059.git-series.maxime@cerno.tech