MIPS: N64: Wire getdents64(2)

As a relatively new ABI, N64 only had getdents syscall while other modern
architectures have getdents64.

This was noticed when Python 3.3 shifted to the latter one for aarch64.

[ralf@linux-mips.org: The history of getdents64 is a little complicated.
Commit 1a1d77dd589de5a567fa95e36aa6999c704ceca4 [Merge with 2.4.0-test7.]
added N64 getdents(2) to arch/mips64/kernel/scall_64.S as syscall 5213,
then dropped again in 578720675c44e54e8aa7c68f6dce59ed37ce3d3b [Overhaul
of the 64-bit syscall interface.  Now heritage free.] for 2.5.18 in 2002.]

Signed-off-by: Aron Xu <aron@debian.org>
Acked-by: David Daney <david.daney@cavium.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/5285/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>