drm/msm: update context locking for 4.14

This change updates the SDE and patched MSM drivers to use
local context locking provided by @drm_modeset_acquire_ctx
since some legacy locking API functions are now deprecated.

Change-Id: I80bf8198a31e1de43f2a1312b4828e5ecb7a3467
Signed-off-by: Steve Cohen <cohens@codeaurora.org>