frv: Use common threadinfo allocator

The core now has a threadinfo allocator which uses a kmemcache when
THREAD_SIZE < PAGE_SIZE.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: David Howells <dhowells@redhat.com>
Link: http://lkml.kernel.org/r/20120505150141.751600045@linutronix.de