mips: Use common threadinfo allocator

No point in using kmalloc for allocating 0, 1 resp. 2 pages for
threadinfo.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Ralf Baechle <ralf@linux-mips.org>
Link: http://lkml.kernel.org/r/20120505150141.936950979@linutronix.de