This api is in linux kernel since version 2.6.39,
and present in all version 3.

The commit that adds the API in master branch of the
linux kernel source is:
https://github.com/torvalds/linux/commit/f8f3914cf922f5f9e1d60e9e10f6fb92742907ad

v4l2 doc: "Some devices require data for each input
or output video frame to be placed in discontiguous
memory buffers"

There are newer structures 'struct v4l2_pix_format_mplane'
and 'struct v4l2_plane'.
So the pixel format is not setup with the same API when using
multi-planar.

Also for gst-v4l2, one of the difference is that in GstV4l2Meta
there are now one mem pointer for each maped plane.

When not using multi-planar, this commit takes care of keeping
the same code path than previously. So that the 2 cases are
in two different blocks triggered from V4L2_TYPE_IS_MULTIPLANAR.

Fixes bug https://bugzilla.gnome.org/show_bug.cgi?id=712754