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>

package/gstreamer1/gst1-imx/Config.in

@@ -87,7 +87,11 @@ config BR2_PACKAGE_GST1_IMX_V4L2VIDEOSRC
 config BR2_PACKAGE_GST1_IMX_V4L2VIDEOSINK
 	bool "imxv4l2videosink"
 	select BR2_PACKAGE_GST1_PLUGINS_BAD
+	depends on BR2_TOOLCHAIN_HEADERS_AT_LEAST_4_2 # V4L2_COLORSPACE_DEFAULT
 	help
 	  Elements for V4L2 output
 
+comment "imxv4l2videosink needs a toolchain w/ headers >= 4.2"
+	depends on !BR2_TOOLCHAIN_HEADERS_AT_LEAST_4_2
+
 endif