drm/vc4: hdmi: Rename full range helper

drm/vc4: hdmi: Rename full range helper

The VC4 HDMI driver has a helper function to figure out whether full
range or limited range RGB is being used called
vc4_hdmi_is_full_range_rgb().

We'll need it to support other colorspaces, so let's rename it to
vc4_hdmi_is_full_range().

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://lore.kernel.org/r/20221207-rpi-hdmi-improvements-v3-4-bdd54f66884e@cerno.tech
Signed-off-by: Maxime Ripard <maxime@cerno.tech>