drm: Drop VGA from bpc definitions

Drop "VGA" from bits per component definitions as these
are also used by other standards such as DVI, HDMI,
DP++.

Reviewed-by: Jim Bride <jim.bride@linux.intel.com>
Signed-off-by: Mika Kahola <mika.kahola@intel.com>
Acked-by: Dave Airlie <airlied@gmail.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1473419458-17080-3-git-send-email-mika.kahola@intel.com