e2fsprogs: disable e4defrag for nios

e4defrag has to be disabled because of the (external) toolchain declares
the fallocate64 call in the header files but don't implement it in the
library. e4defrag defines its own fallocate64 function that throws an
error because of the previous declaration in the toolchain header.

Signed-off-by: Frank Bergmann <frank@frajasalo.de>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>