media: ipu3-imgu: Use MENU type for mode control

This addresses the below TODO item.
- Use V4L2_CTRL_TYPE_MENU for dual-pipe mode control. (Sakari)

Signed-off-by: Yong Zhi <yong.zhi@intel.com>
Reviewed-by: Tomasz Figa <tfiga@chromium.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>