gpio/mpc8xxx: fix qoriq GPIO reading

Qoriq requires the IBE register to be set to enable GPIO inputs to be
read.  Set it.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Link: https://lore.kernel.org/r/E1iX3HC-00069N-0T@rmk-PC.armlinux.org.uk


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>