drm/fourcc: Add format info helpers for checking YUV sub-sampling

Display engine drivers often need to distinguish between different types of
YUV sub-sampling. This introduces helpers to check for common sub-sampling
ratios in their commonly-used denomination from the DRM format info.

Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Reviewed-by: Maxime Ripard <maxime.ripard@bootlin.com>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190118145133.21281-3-paul.kocialkowski@bootlin.com