video: mmp: calculate pitch value when fb set win

Add new func mmpfb_set_win to make code clean, it will do resolution
and fmt setting of win in mmpfb_set_win.

Signed-off-by: Jing Xiang <jxiang@marvell.com>
Signed-off-by: Jett.Zhou <jtzhou@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>