media: i2c: imx477: Add vsync trigger_mode parameter

trigger_mode == 0 (default) => no effect / no registers written
trigger_mode == 1           => source
trigger_mode == 2           => sink

This can be set e.g. in /boot/cmdline.txt as imx477.trigger_mode=N

Signed-off-by: Jonas Jacob <jonas.jacob@neocortexvision.com>