connman: disable for sparc

Fixes:
http://autobuild.buildroot.net/results/333/3336df777c758cba9a660a0f6f31646258baec52/
http://autobuild.buildroot.net/results/efe/efeb197654b552ad9a80e102226c3e507640f037/



Connman uses __sync_fetch_and_add, which is not available for sparc.

[Peter: add !sparc dependency to comment, add autobuild reference]
Signed-off-by: Waldemar Brodkorb <wbx@openadk.org>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>