NFS: Clean up writeback code

Now that the VM promises never to recurse back into the filesystem
layer on writeback, remove all the GFP_NOFS references etc from
the generic writeback code.

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

fs/nfs/pnfs.c

@@ -2468,7 +2468,7 @@ pnfs_generic_pg_init_write(struct nfs_pageio_descriptor *pgio,
 						   wb_size,
 						   IOMODE_RW,
 						   false,
-						   GFP_NOFS);
+						   GFP_KERNEL);
 		if (IS_ERR(pgio->pg_lseg)) {
 			pgio->pg_error = PTR_ERR(pgio->pg_lseg);
 			pgio->pg_lseg = NULL;