drm/stm: ltdc: add YCbCr 422 output support

drm/stm: ltdc: add YCbCr 422 output support

LTDC 40100 hw version supports the YCbCr 422 output,
reducing the output pins from 24 to 16. This feature
is useful for some external devices like HDMI bridges.

Both ITU-R BT.601 & ITU-R BT.709 are supported.

It is also possible to choose the chrominance order between
* Cb is output first (Y0Cb, then Y1Cr, Y2Cb and so on).
* Cr is output first (Y0Cr, then Y1Cb, Y2Cr and so on).

Signed-off-by: Yannick Fertre <yannick.fertre@foss.st.com>
Acked-by: Philippe Cornu <philippe.cornu@foss.st.com>
Reviewed-by: Philippe Cornu <philippe.cornu@foss.st.com>
Reviewed-by: Raphael Gallais-Pou <raphael.gallais-pou@foss.st.com>
Signed-off-by: Philippe Cornu <philippe.cornu@foss.st.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211215214750.20105-1-yannick.fertre@foss.st.com