ARM: pxa: call debug_ll_io_init for earlyprintk

This is already done automatically for many other ARM platforms by the
ARM core code, but since pxa is using the .map_io callback, it needs to
call it explicitely for earlyprintk support.

Signed-off-by: Andrew Ruder <andrew.ruder@elecsyscorp.com>
Acked-by: Haojian Zhuang <haojian.zhuang@linaro.org>