[media] s5p-fimc: Add missing FIMC-LITE file operations locking

commit 5126f259
"v4l2-dev: add flag to have the core lock all file operations"
introduced an additional bit flag (V4L2_FL_LOCK_ALL_FOPS) that
should be set by drivers that use the v4l2 core lock for all file
operations. Since this driver has been merged at the same time as
the core changes it doesn't set this flags and thus its all file
operations except IOCTL are not properly serialized. Fix this by
adding file ops locking in the driver.

Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>