V4L/DVB (10072): soc-camera: Add signal inversion flags to be used by camera drivers

As reported by Antonio Ospite <ospite@studenti.unina.it> two platforms with a
mt9m111 camera require opposite pixel clock polarity, which means one of them
inverts it. This patch adds support for inversion flags and switches all
available camera drivers to using them.

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