libnss: Disable for MIPS64 n32 platforms

This package fails to compile for MIPS64 n32 platforms. We are in
conversations with upstream to fix this problem. Meanwhile we disable
this package until we fix it.

Fixes:
   http://autobuild.buildroot.net/results/0e3/0e3f1482d6f2f9bddc53d4e78b575120a2729e1d/



Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>