video: mmp: optimize some register setting code

There are dumplicate code of the smooth setting based on different
path, optimized the routine and use readl_relaxed instead.

Signed-off-by: Jett.Zhou <jtzhou@marvell.com>
Signed-off-by: Jing Xiang <jxiang@marvell.com>
Signed-off-by: Guoqing Li <ligq@marvell.com>
Signed-off-by: Zhou Zhu <zzhu3@marvell.com>
Reviewed-by: Daniel Drake <dsd@laptop.org>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>