staging: lustre: libcfs: simplify memory allocation.

1/ Use kvmalloc() instead of kmalloc or vmalloc
2/ Discard the _GFP() interfaces that are never used.
  We only ever do GFP_NOFS and GFP_ATOMIC allocations,
  so support each of those explicitly.

Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>