drm/vc4: Add HDR metadata property to the VC5 HDMI connectors

Now that we can export deeper colour depths, add in the signalling
for HDR metadata.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20210430094451.2145002-3-maxime@cerno.tech