bayer: Caps for 16-bit Bayer

Submitted by Joshua M. Doe

Link to original bug (#693666)

Description

Currently in both 0.10 and 1.0 the caps for Bayer are limited to 8-bits, however 16-bit is quite common, and I've seen 12-bit as well. I have seen three different ways to extend this to at least 16-bit:

1. I have used video/x-raw-bayer,format=(string){gbrg16, bggr16, grbg16, rggb16} so as to not conflict with the current expectation of 8-bit data from bayer2rgb and rgb2bayer. Alternatively, something like video/x-raw-bayer16 could work as well, if not an elegant solution.

2. gst-plugins-elphel has a "bpp" property in their bayer2rgb2 element which when true assumes the data to be 16-bit, otherwise 8-bit:
   http://code.google.com/p/gst-plugins-elphel/source/browse/trunk/bayer2rgb2/src/gstbayer2rgb2.c#267

3. Aravis simply adds bpp and depth to the video/x-raw-bayer caps:
   http://git.gnome.org/browse/aravis/tree/src/arvmisc.c#n635
   #2 is clearly not a good solution since it moves the bpp out of the caps. #3 is the most robust solution, though it would mean some applications would break, though if supporting elements always prioritize bpp=8,depth=8, then breakage would be minimal I believe. If changing the existing caps are unacceptable, then we'd have to go with #1.