of: create of_phandle_args to simplify return of phandle parsing data

of_parse_phandle_with_args() needs to return quite a bit of data.  Rather
than making each datum a separate **out_ argument, this patch creates
struct of_phandle_args to contain all the returned data and reworks the
user of the function.  This patch also enables of_parse_phandle_with_args()
to return the device node pointer for the phandle node.

This patch also ends up being fairly major surgery to
of_parse_handle_with_args().  The existing structure didn't work well
when extending to use of_phandle_args, and I discovered bugs during testing.
I also took the opportunity to rename the function to be like the
existing of_parse_phandle().

v2: - moved declaration of of_phandle_args to fix compile on non-DT builds
    - fixed incorrect index in example usage
    - fixed incorrect return code handling for empty entries

Reviewed-by: Shawn Guo <shawn.guo@freescale.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

include/linux/of_gpio.h

@@ -18,6 +18,7 @@
 #include <linux/kernel.h>
 #include <linux/errno.h>
 #include <linux/gpio.h>
+#include <linux/of.h>
 
 struct device_node;
 
@@ -57,8 +58,9 @@ extern int of_mm_gpiochip_add(struct device_node *np,
 extern void of_gpiochip_add(struct gpio_chip *gc);
 extern void of_gpiochip_remove(struct gpio_chip *gc);
 extern struct gpio_chip *of_node_to_gpiochip(struct device_node *np);
-extern int of_gpio_simple_xlate(struct gpio_chip *gc, struct device_node *np,
-				const void *gpio_spec, u32 *flags);
+extern int of_gpio_simple_xlate(struct gpio_chip *gc,
+				const struct of_phandle_args *gpiospec,
+				u32 *flags);
 
 #else /* CONFIG_OF_GPIO */
 
@@ -75,8 +77,8 @@ static inline unsigned int of_gpio_count(struct device_node *np)
 }
 
 static inline int of_gpio_simple_xlate(struct gpio_chip *gc,
-				       struct device_node *np,
-				       const void *gpio_spec, u32 *flags)
+				       const struct of_phandle_args *gpiospec,
+				       u32 *flags)
 {
 	return -ENOSYS;
 }