gpio: iop: Use generic GPIO MMIO functions for driver

This patch switches the driver to use the generic GPIO MMIO functions
that removes a bit of redundant and duplicate code.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index 17842e6a..68c2d647 100644
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -228,7 +228,8 @@
 
 config GPIO_IOP
 	tristate "Intel IOP GPIO"
-	depends on ARM && (ARCH_IOP32X || ARCH_IOP33X)
+	depends on ARCH_IOP32X || ARCH_IOP33X || COMPILE_TEST
+	select GPIO_GENERIC
 	help
 	  Say yes here to support the GPIO functionality of a number of Intel
 	  IOP32X or IOP33X.