drm/modes: Introduce drm_mode_match()

Make mode matching less confusing by allowing the caller to specify
which parts of the modes should match via some flags.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Shashank Sharma <shashank.sharma@intel.com>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1525777785-9740-2-git-send-email-ankit.k.nautiyal@intel.com