media: v4l2-tpg-core: Add 16-bit bayer

Add 16-bit bayer formats to the test pattern generator, namely
  V4L2_PIX_FMT_SRGGB16
  V4L2_PIX_FMT_SGRBG16
  V4L2_PIX_FMT_SGBRG16
  V4L2_PIX_FMT_SBGGR16

Signed-off-by: Bård Eirik Winther <bwinther@cisco.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>