media: videobuf2: handle V4L2_FLAG_MEMORY_NON_CONSISTENT flag

This patch lets user-space to request a non-consistent memory
allocation during CREATE_BUFS and REQBUFS ioctl calls.

= CREATE_BUFS

  struct v4l2_create_buffers has seven 4-byte reserved areas,
  so reserved[0] is renamed to ->flags. The struct, thus, now
  has six reserved 4-byte regions.

= CREATE_BUFS32

  struct v4l2_create_buffers32 has seven 4-byte reserved areas,
  so reserved[0] is renamed to ->flags. The struct, thus, now
  has six reserved 4-byte regions.

= REQBUFS

 We use one bit of a ->reserved[1] member of struct v4l2_requestbuffers,
 which is now renamed to ->flags. Unlike v4l2_create_buffers, struct
 v4l2_requestbuffers does not have enough reserved room. Therefore for
 backward compatibility  ->reserved and ->flags were put into anonymous
 union.

Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>