[media] V4L: soc-camera: add 2 new ioctl() handlers

This patch adds two new ioctl() handlers: .vidioc_create_bufs() and
.vidioc_prepare_buf() for compliant vb2 soc-camera hosts.

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