drm/i915: Add support for the YCbCr COLOR_ENCODING property

Add support for the COLOR_ENCODING plane property which selects
the matrix coefficients used for the YCbCr->RGB conversion. Our
hardware can generally handle BT.601 and BT.709.

CHV pipe B sprites have a fully programmable matrix, so in theory
we could handle anything, but it doesn't seem all that useful to
expose anything beyond BT.601 and BT.709 at this time.

GLK can supposedly do BT.2020, but let's leave enabling that for
the future as well.

v2: Rename bit defines to match the spec more closely (Shashank)

Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Daniel Stone <daniel@fooishbar.org>
Cc: Russell King - ARM Linux <linux@armlinux.org.uk>
Cc: Ilia Mirkin <imirkin@alum.mit.edu>
Cc: Hans Verkuil <hverkuil@xs4all.nl>
Cc: Uma Shankar <uma.shankar@intel.com>
Cc: Shashank Sharma <shashank.sharma@intel.com>
Cc: Jyri Sarha <jsarha@ti.com>
Reviewed-by: Shashank Sharma <shashank.sharma@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180214192327.3250-7-ville.syrjala@linux.intel.com