powerpc/QE: move QE_GPIO Kconfig symbol into the platforms/Kconfig

Specifying user-selectable option in the qe_lib/Kconfig was a bad idea
because the qe_lib/Kconfig is included into the top level Kconfig, and
thus the QE_GPIO option appears at the top level menu.

This patch effectively moves the QE_GPIO option under the platform menu
instead.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>