V4L/DVB (11031): pcm990 baseboard: add camera bus width switch setting

Some Phytec cameras have a I2C GPIO expander which allows it to
switch between different sensor bus widths. This was previously
handled in the camera driver. Since handling of this switch
varies on several boards the cameras are used on, the board
support seems a better place to handle the switch

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