Given Andi Kleen's patch that introduces of VFS-level support for
nanosecond time resolutions, we should finally be able to export the
existing NFS client level support to userland.

In order to do so, the following patch will convert all NFS private 'raw
u64' values into the kernel-supported struct timespec directly in the
xdr_encode/xdr_decode routines.

It adds support for the nanosecond field in NFS 'setattr' calls, and in
nfs_refresh_inode().

Finally, there are a few cleanups in the nfs_refresh_inode code that
convert multiple use of the NFS_*(inode) macros into a single
dereference of NFS_I(inode).