gpio: Fix OF build problem on UM

gpio: Fix OF build problem on UM

commit 2527ecc9195e9c66252af24c4689e8a67cd4ccb9 upstream.

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: Geert Uytterhoeven <geert@linux-m68k.org>
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>