staging/bcm2835-codec: Implement additional g_selection calls for decode

v4l_cropcap calls our vidioc_g_pixelaspect function to get the pixel
aspect ratio, but also calls g_selection for V4L2_SEL_TGT_CROP_BOUNDS
and V4L2_SEL_TGT_CROP_DEFAULT. Whilst it allows for vidioc_g_pixelaspect
not to be implemented, it doesn't allow for either of the other two.

Add in support for the additional selection targets.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>