imx477: Update device tree overlays to support trigger-mode

Also create generic overrides in camera-mux-N-port, that can be extended
to configure vsync modes for cameras supporting this.

Example usages (to be combined with camera_auto_detect=0):
dtoverlay=imx477,cam0,sync-source
dtoverlay=imx477,sync-sink
dtoverlay=camera-mux-2port,cam1-imx477,cam1-sync-sink
dtoverlay=camera-mux-4port,cam3-imx477,cam3-sync-sink

Signed-off-by: Erik Botö <erik.boto@gmail.com>