crda: disable on NIOS II

Building crda on NIOS II triggers the infamous _gp linker issue. Since
nobody cared, let's disable this package on NIOS II for the moment.

Fixes:

  http://autobuild.buildroot.net/results/272/272f18410e4855ab6b3bfd8a44243c1ebecf6abe/



Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>