drm/edid: parse ycbcr 420 deep color information

CEA-861-F spec adds ycbcr420 deep color support information
in hf-vsdb block. This patch extends the existing hf-vsdb parsing
function by adding parsing of ycbcr420 deep color support from the
EDID and adding it into display information stored.

V2: Rebase
V3: Rebase
V4: Moved definition of y420_dc_modes into this patch, where its used
    (Ville)
V5: Optimize function, if(conditions) not reqd (Ville)
V6: Rebase
V7: Rebase

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Jose Abreu <joabreu@synopsys.com>
Signed-off-by: Shashank Sharma <shashank.sharma@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1499960000-9232-8-git-send-email-shashank.sharma@intel.com


[vsyrjala: Fix sparse indentation warn]
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>