gpio: Fix OF build problem on UM

The UserMode (UM) Linux build was failing in gpiolib-of as it requires
ioremap()/iounmap() to exist, which is absent from UM. The non-existence
of IO memory is negatively defined as CONFIG_NO_IOMEM which means we
need to depend on HAS_IOMEM.

Cc: stable@vger.kernel.org
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/Kconfig

@@ -50,6 +50,7 @@ config GPIO_DEVRES
 config OF_GPIO
 	def_bool y
 	depends on OF
+	depends on HAS_IOMEM
 
 config GPIO_ACPI
 	def_bool y