drivers: media: i2c: imx296,imx477: Configure tigger_mode every time

Don't assume the camera has been reset each time we start streaming,
but always write registers relating to trigger_mode, even in mode 0.

IMX477: Stop driving XVS on stop streaming, to avoid spurious pulses.

Signed-off-by: Nick Hollinghurst <nick.hollinghurst@raspberrypi.com>