GFX-Display: detach overlay rw ioctrl, gtt map/umap ioctrl from drm global lock.

GFX-Display: detach overlay rw ioctrl, gtt map/umap ioctrl from drm global lock.

BZ: 38361

1. Gtt map/unmap ioctrl don't need hold drm global lock. There is already a mm lock
for protecting gtt mm resource.
2. overlay wait vblank function should not block on mode_config lock, that will cause
actual wait time exceed a vblank period.
3. Add a mutex to protect overlay rw ioctrl instead of drm global lock. Because this
ioctrl is only used by overlay, it is not necessary to lock other display registers.

Change-Id: Ic9f98fb5bcb28925740133a4fb0c0aa3679b25ac
Signed-off-by: Jason Hu <jason.hu@intel.com>
Reviewed-on: http://android.intel.com:8080/52606
Reviewed-by: Ding, Haitao <haitao.ding@intel.com>
Tested-by: Ding, Haitao <haitao.ding@intel.com>
Reviewed-by: buildbot <buildbot@intel.com>
Tested-by: buildbot <buildbot@intel.com>