V4L/DVB (8343): soc_camera_platform: Add SoC Camera Platform driver

This patch adds a simple platform camera device. Useful for testing
cameras with SoC camera host drivers. Only one single pixel format
and resolution combination is supported.

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>