gpsd: requires shared library support

gpsd always tries to build a shared library, so make it 'depends on
!BR2_STATIC_LIBS'. We also propagate this to the only gpsd reverse
dependency, the location support of sconeserver. While we're at it, we
add a comment indicating the dependencies of this location support,
which was missing.

Fixes:

  http://autobuild.buildroot.org/results/f52/f5261a0933f9b5449d1f4e5cab1bb02e7154e683/



Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>