V4L/DVB (8339): soc_camera: Add 16-bit bus width support

The SuperH Mobile CEU hardware supports 16-bit width bus,
so extend the soc_camera code with SOCAM_DATAWIDTH_16.

Signed-off-by: Magnus Damm <damm@igel.co.jp>
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@pengutronix.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>