[MIPS] txx9: Make gpio_txx9 entirely spinlock-safe

TXx9 GPIO set/get routines are spinlock-safe.  This patch make
gpio_direction_{input,output} routines also spinlock-safe so that they
can be used during early board setup.

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>