We parse the EDID and add all the modes in the connector's modelist.
This adds CEA modes with aspect ratio information too, regardless of
whether user space requested this information or not.

This patch:
-prunes the modes with aspect-ratio information, from the
 drm_mode_get_connector modelist supplied to the user, if the
 user-space has not set the aspect ratio DRM client cap. However if
 such a mode is unique in the list, it is kept in the list, with
 aspect-ratio flags reset.
-prepares a list of exposed modes, which is used to find unique modes
 if aspect-ratio is not allowed.
-adds a new list_head 'exposed_head' in drm_mode_display, to traverse
 the list of exposed modes.

Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Cc: Shashank Sharma <shashank.sharma@intel.com>
Cc: Jose Abreu <jose.abreu@synopsys.com>
Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>

V3: As suggested by Ville, modified the mechanism of pruning of modes
    with aspect-ratio, if the aspect-ratio is not supported. Instead
    of straight away pruning such a mode, the mode is retained with
    aspect ratio bits set to zero, provided it is unique.
V4: rebase
V5: Addressed review comments from Ville:
    -used a pointer to store last valid mode.
    -avoided, modifying of picture_aspect_ratio in kernel mode,
     instead only flags bits of user mode are reset (if aspect-ratio
     is not supported).
V6: As suggested by Ville, corrected the mode pruning logic and
    elaborated the mode pruning logic and the assumptions taken.
V7: rebase
V8: rebase
V9: rebase
V10: rebase
V11: Fixed the issue caused in kms_3d test, and enhanced the pruning
     logic to correctly identify and prune modes with aspect-ratio,
     if aspect-ratio cap is not set.
V12: As suggested by Ville, added another list_head in
     drm_mode_display to traverse the list of exposed modes and
     avoided duplication of modes.
V13: Minor modifications, as suggested by Ville.
v14: As suggested by Daniel Vetter and Ville Syrjala, corrected the
     pruning logic to avoid any dependency in the order of mode with
     aspect-ratio.
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1525777785-9740-9-git-send-email-ankit.k.nautiyal@intel.com