drm/vc4: drop unnecessary and harmful HDMI RGB format check

RGB is a mandatory format for all DVI and HDMI monitors so there's
no need to check for presence of the DRM_COLOR_FORMAT_RGB444 bit in
color_formats.

More importantly this checks breaks working around EDID issues with
eg video=HDMI-A-1:1024x768D or drm.edid_firmware=edid/1024x768.bin
as the RGB444 bit is only set when a valid EDID with digital bit set in
the input byte is present - which isn't the case when no EDID can be
read from the display device at all or with the in-built kernel EDIDs,
which mimic analog (VGA) displays without the digital bit set.

So drop the check, if we output video on the HDMI connector we can
assume that the display can accept 8bit RGB.

Signed-off-by: Matthias Reichl <hias@horus.com>