channel/tsmf: fixed gstreamer plugin build

Gstreamer wasn't build because it requires xrandr which wasn't
detected.

Fixes #1146
channel/tsmf: fix for gstreamer detection

Print warning if gstreamer is there but xrandr is missing.
Merge pull request #1147 from bmiklautz/issue_1146

channel/tsmf: fixed gstreamer plugin build