gst1-imx: add missing dependency for imxv4l2videosink plugin

gst1-imx: add missing dependency for imxv4l2videosink plugin

The plugin source code uses V4L2_COLORSPACE_DEFAULT macro which was
defined in kernel 4.2, so make sure the toolchain headers match this
requirement.

Fixes:
http://autobuild.buildroot.net/results/48dd782161fa5e8860b5ea00a5d60207cb623108/
http://autobuild.buildroot.net/results/f970c782b5bfbcf66ff3ba200b060d3653ff2630/

Signed-off-by: Gary Bisson <gary.bisson@boundarydevices.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>