drm/vc4: hdmi: Signal the proper colorimetry info in the infoframe

Our driver while supporting HDR didn't send the proper colorimetry info
in the AVI infoframe.

Let's add the property needed so that the userspace can let us know what
the colorspace is supposed to be.

Reviewed-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20210430094451.2145002-5-maxime@cerno.tech