dm: exynos: Tidy up GPIO headers

The wrong header is being included, thus requiring the code to re-declare
the generic GPIO interface in each GPIO header.

Fix this.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/arm/cpu/armv7/exynos/pinmux.c b/arch/arm/cpu/armv7/exynos/pinmux.c
index b929486..2caeb3e 100644
--- a/arch/arm/cpu/armv7/exynos/pinmux.c
+++ b/arch/arm/cpu/armv7/exynos/pinmux.c
@@ -7,7 +7,7 @@
 
 #include <common.h>
 #include <fdtdec.h>
-#include <asm/arch/gpio.h>
+#include <asm/gpio.h>
 #include <asm/arch/pinmux.h>
 #include <asm/arch/sromc.h>