drm/msm: defer DSI panel timing parameter parsing

For each display,  DRM maintains DRM modes which corresponds
to the timing data supported by the panel. There can be more
than one panel timings supported by a panel. This change groups
bindings related to panel timings and defers parsing them until
DRM queries for supported modes. All driver specific timing
parameters of the mode are maintained in the private field of
the DRM mode. On display mode_set, SDE driver queries the
DSI driver to get custom information on the display mode set.
On display mode_set, SDE queries respective display driver to
get custom information on the mode programmed.

Change-Id: I0f63ac655a714f2e3bc1ed366de9661b2810d0a5
Signed-off-by: Jeykumar Sankaran <jsanka@codeaurora.org>