drm: add picture aspect ratio flags

This patch adds drm flag bits for aspect ratio information

Currently drm flag bits don't have field for mode's picture
aspect ratio. This field will help the driver to pick mode with
right aspect ratio, and help in setting right VIC field in avi
infoframes.

V2: Addressed review comments from Sean
- Changed PAR-> PIC_AR
V3: Rebase
V3: Added r-b by Jose

Signed-off-by: Shashank Sharma <shashank.sharma@intel.com>
Reviewed-by: Jim Bride <jim.bride@linux.intel.com>
Reviewed-by: Jose Abreu <Jose.Abreu@synopsys.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Emil Velikov <emil.l.velikov@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1476705880-15600-2-git-send-email-shashank.sharma@intel.com