ARM: ux500: CONFIG: Enable GPIO Regulators

It is the intention to convert the MMC voltage changing from
GPIO flipping to using a proper GPIO regulator interface. A
prerequisite of that is to enable the GPIO regulator
functionality. As this affects all ux5x0 based boards we'll
do it here instead of in the Kconfigs.

Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>