fio: disable on nios2 because of missing fallocate64()

The fallocate() function is replaced by fallocate64() while compiling
with LARGE_FILE flags. Current nios2 toolchain is missing the fallocate64()
function.

Fixes:
    http://autobuild.buildroot.net/results/9cd/9cd30031a40f768f6090cfba44c880fb2406672b
    http://autobuild.buildroot.net/results/7da/7da32ca8178aa6bada06dfaea38e9e693fba0db2
    http://autobuild.buildroot.net/results/0ef/0ef7358289bff2a5f9efda27115eddb379c1a0b9


    [...]

[Peter: reference BR2_LARGEFILE, add autobuilder refs as suggested by Yann]
Signed-off-by: Frank Bergmann <frank@frajasalo.de>
Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>