powerpc/p3060qds: Fix select of 'MPC8xxx_GPIO'

The driver for the Freescale P3060 QDS got added by commit 96cc017c
("[...] Add support for P3060QDS board"). Its Kconfig entry selects
MPC8xxx_GPIO. But at the time that driver got added MPC8xxx_GPIO was
already renamed to GPIO_MPC8XXX, by commit c68308dd

 ("gpio: move
mpc8xxx/512x gpio driver to drivers/gpio").

So make this driver select GPIO_MPC8XXX.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Acked-by: Wolfram Sang <w.sang@pengutronix.de>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>