V4L/DVB (12171): em28xx: fix webcam usage with different output formats

Discovered the bug that were limiting the output format to just RGB565.
Now, it is possible to output image at Bayer format (the original one,
as generated by Silvercrest sensor, and two others), and also on YUY.

Adds Bayer formats also to the driver.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>