gpio: mxs: use enable/disable regs to (un)mask irqs

gpio: mxs: use enable/disable regs to (un)mask irqs

The mxs gpio controller does not only have a mask register to mask
interrupts, but also enable/disable registers. Use the enable/disable
registers rather than the mask register. This does not have any
advantage for now, but makes the next patch simpler.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Reviewed-by: Marek Vasut <marex@denx.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>