drm/msm: propagate mode private data without mode_config mutex

Cache DSI modes in the DSI driver, and move private mode data
data propagation within the Bridge mode fixup callback.This
avoids requiring the DRM mode_config mutex lock to iterate over
the connector mode lists when retrieving the probed mode private
data. The mode_config mutex must be taken, but cannot be taken
in all paths since it is taken by non-atomic commits.

Change-Id: I80c36f94c593ecde0f7338a431af3147e4634291
Signed-off-by: Lloyd Atkinson <latkinso@codeaurora.org>