NFS: Convert GFP_NOFS to GFP_KERNEL

Assume that sections that should not re-enter the filesystem are already
protected with memalloc_nofs_save/restore call, so relax those GFP_NOFS
instances which might be used by other contexts.

Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>