sandbox: gpio: add basic driver for simulating GPIOs

This provides a way of simulating GPIOs by setting values which are seen
by the normal gpio_get/set_value() calls.

Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
diff --git a/drivers/gpio/Makefile b/drivers/gpio/Makefile
index 4375a55..fb3b09a 100644
--- a/drivers/gpio/Makefile
+++ b/drivers/gpio/Makefile
@@ -34,6 +34,7 @@
 COBJS-$(CONFIG_PCA953X)		+= pca953x.o
 COBJS-$(CONFIG_PCA9698)		+= pca9698.o
 COBJS-$(CONFIG_S5P)		+= s5p_gpio.o
+COBJS-$(CONFIG_SANDBOX_GPIO)	+= sandbox.o
 COBJS-$(CONFIG_TEGRA2_GPIO)	+= tegra2_gpio.o
 COBJS-$(CONFIG_DA8XX_GPIO)	+= da8xx_gpio.o
 COBJS-$(CONFIG_ALTERA_PIO)	+= altera_pio.o