contrib/rpm: exclude device plugins for ADSL and Wi-Fi on s390

contrib/rpm: exclude device plugins for ADSL and Wi-Fi on s390

s390 does not enable several device plugins, but ADSL and Wi-Fi
plugins are still build. They must be excluded in the spec file,
otherwise rpmbuild fails.

This partly reverts commit 1f631cd08d0f01cd118e7222822518d62916f117.

  Checking for unpackaged file(s): /usr/lib/rpm/check-files /builddir/build/BUILDROOT/NetworkManager-1.1.0-11242.9709d009d5.el7.s390x
  RPM build errors:
  error: Installed (but unpackaged) file(s) found:
     /usr/lib64/NetworkManager/libnm-device-plugin-adsl.so
     /usr/lib64/NetworkManager/libnm-device-plugin-wifi.so
      Installed (but unpackaged) file(s) found:
     /usr/lib64/NetworkManager/libnm-device-plugin-adsl.so
     /usr/lib64/NetworkManager/libnm-device-plugin-wifi.so
  Child returncode was: 1