omgps: add libcap dependency

http://lists.openembedded.org/pipermail/openembedded-core/2013-August/082530.html



Omgps links against libcap without checking the library. If it cannot
find it as in the minimal build, it emits an error in the linking stage.
Add the dependency explicitly.

Signed-off-by: Eren Türkay <eren@hambedded.org>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>