drm/i915: set colorspace for YCBCR420 outputs

When output colorspace is YCBCR420, we have to load the
corresponding colorspace in AVI infoframe. This patch fills
the colorspace of AVI infoframe as per the output mode.

V2: Rebase
V3: Rebase
V4: Rebase
V5: Added r-b from Ander
V6: Checking RGB/YCBCR420 output only (Ville)
V7: Add colorspace info in driver(not drm layer) (Ville)
V8: Rebase
V9: Added r-b from Ville
V10: Added r-b from Imre

Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Cc: Ander Conselvan de Oliveira <conselvan2@gmail.com>
Cc: Imre Deak <imre.deak@intel.com>

Reviewed-by: Ander Conselvan de Oliveira <conselvan2@gmail.com>
Reviewed-by: Ville Syrjala <ville.syrjala@linux.intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Shashank Sharma <shashank.sharma@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1500650709-14447-6-git-send-email-shashank.sharma@intel.com


Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>