V4L/DVB (10087): Add new enum_input function on soc_camera

This patch presents new method to be able to select V4L2 input type

Signed-off-by: Kuninori Morimoto <morimoto.kuninori@renesas.com>
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>