cris: Use common threadinfo allocator

There is no functional difference. __get_free_pages() ends up calling
alloc_pages_node().

This also allocates only one page which matches THREAD_SIZE instead of
an extra page for nothing.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Jesper Nilsson <jesper.nilsson@axis.com>
Link: http://lkml.kernel.org/r/20120505150141.681236240@linutronix.de