gpsd: disable for microblaze arch

gpsd will fail on an internal compiler error for the microblaze
architecture so disabling it on that architecture.

Fixes:
  http://autobuild.buildroot.org/results/42d/42da870722f24e4202d8265597771a0449e74cfd



[Peter: add comment explaining why]
Signed-off-by: Ryan Barnett <rjbarnet@rockwellcollins.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>