drm/msm/sde: track mode information in connector state

With dynamic mode switch enabled, client can switch the DRM mode
of the display while the current frame configuration is ongoing.
Maintaining the mode information in encoder object may demand
synchronization between client and display threads to avoid
data overlap due race conditions. This change moves the mode info
to atomic connector state so the data will not be visible to
the display thread until state swap is done.

Change-Id: I303b459fe710acf870fc82539e778beb88a80d3f
Signed-off-by: Jeykumar Sankaran <jsanka@codeaurora.org>