package/samba{,4}: disable on nios2

samba produces particularly large binaries, and the relocations needed
for it do not fit in the possible relocation mechanisms available on
nios2. Since samba is very unlikely to be used on nios2, let's just
disable it, as we've done for AVR32.

Fixes:
    http://autobuild.buildroot.net/results/7b9/7b9dcb537f98714fe57fe384ecbb49bd9ae52aee/



Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Gustavo Zacarias <gustavo@zacarias.com.ar>
Acked-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>