c6x: Use common threadinfo allocator

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

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Mark Salter <msalter@redhat.com>
Link: http://lkml.kernel.org/r/20120505150141.621728944@linutronix.de