m32r: Use common threadinfo allocator

No reason why m32r needs to use kmalloc to allocate 2 pages instead of
using the core allocator.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Hirokazu Takata <takata@linux-m32r.org>
Link: http://lkml.kernel.org/r/20120505150141.875430830@linutronix.de