drm: Fix EDID color format parsing

The code should obviously check the EDID feature field for EDID feature flags
and not the color_formats field of the drm_display_info struct. Also update the
color_formats field with new modes instead of overwriting the current mode.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Reviewed-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>