[media] s5p-mfc: Use clock gating only on MFC v5 hardware

Newer MFC hardware have internal clock gating feature, so additional
software-triggered clock gating sometimes causes misbehavior of the MFC
firmware and results in freeze or crash. This patch changes the driver
to use software-triggered clock gating only when working with v5 MFC
hardware, where it has been proven to work properly.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>