[media] V4L: soc-camera: compatible bus-width flags

With the new subdevice media-bus configuration methods bus-width is not
configured along with other bus parameters, instead, it is derived from
the data format. With those methods it is convenient to specify
supported bus-widths in the platform data as (1 << (width - 1)). We
redefine SOCAM_DATAWIDTH_* flags to use the same convention to make
platform data seemlessly reusable.

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