MIPS: Wire up statx system call

Wire up the statx system call for MIPS, which was introduced in commit
a528d35e

 ("statx: Add a system call to make enhanced file info
available").

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/15387/


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