drm/edid: Populate picture aspect ratio for CEA modes

Adding picture aspect ratio for CEA modes based on CEA-861D Table 3 or
CEA-861E Table 4. This is useful for filling up the detail in AVI
infoframe.

v2: Ville's review comments incorporated
Added picture aspect ratio as part of edid_cea_modes instead of DRM_MODE

Signed-off-by: Vandana Kannan <vandana.kannan@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>