Since the commit "gpio: mvebu: switch to regmap for register access" the
driver use the regmap. Explicitly select the REGMAP_MMIO symbol to fix
build error.
Reported-by: Nkbuild test robot <fengguang.wu@intel.com>
Signed-off-by: NGregory CLEMENT <gregory.clement@free-electrons.com>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>