i.MX31: add a simple gpio driver

This is a minimal driver, so far only managing output. It will
be used by the mxc_spi.c driver.

Signed-off-by: Guennadi Liakhovetski <lg@denx.de>
Acked-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
diff --git a/drivers/gpio/Makefile b/drivers/gpio/Makefile
index dd618ed..f10144f 100644
--- a/drivers/gpio/Makefile
+++ b/drivers/gpio/Makefile
@@ -25,7 +25,8 @@
 
 LIB 	:= $(obj)libgpio.a
 
-COBJS-$(CONFIG_PCA953X)	+= pca953x.o
+COBJS-$(CONFIG_MX31_GPIO)	+= mx31_gpio.o
+COBJS-$(CONFIG_PCA953X)		+= pca953x.o
 
 COBJS	:= $(COBJS-y)
 SRCS 	:= $(COBJS:.o=.c)