[media] s5p-mfc: keep RISC ON during reset for V7/V8

Reset sequence for MFC V7 and V8 do not need RISC_ON
to be set to 0, while for MFC V6 it is still needed.

Also, remove a couple of register settings during Reset
which are not needed from V6 onwards.

Signed-off-by: Kiran AVND <avnd.kiran@samsung.com>
Signed-off-by: Arun Kumar K <arun.kk@samsung.com>
Signed-off-by: Kamil Debski <k.debski@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>