of_gpio: Should use new <linux/gpio.h> header

Since commit 7560fa60 (gpio: <linux/gpio.h>
and "no GPIO support here" stubs) drivers can use GPIOs if they're available,
but don't require them.

This patch actually enables this feature.
Signed-off-by: Wolfgang Grandegger <wg@grandegger.com>
Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

include/linux/of_gpio.h

@@ -15,7 +15,7 @@
 #define __LINUX_OF_GPIO_H
 
 #include <linux/errno.h>
-#include <asm/gpio.h>
+#include <linux/gpio.h>
 
 #ifdef CONFIG_OF_GPIO