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/asm-generic/gpio.h

@@ -4,6 +4,7 @@
 #include <linux/kernel.h>
 #include <linux/types.h>
 #include <linux/errno.h>
+#include <linux/of.h>
 
 #ifdef CONFIG_GPIOLIB
 
@@ -128,8 +129,8 @@ struct gpio_chip {
 	 */
 	struct device_node *of_node;
 	int of_gpio_n_cells;
-	int (*of_xlate)(struct gpio_chip *gc, struct device_node *np,
-		        const void *gpio_spec, u32 *flags);
+	int (*of_xlate)(struct gpio_chip *gc,
+		        const struct of_phandle_args *gpiospec, u32 *flags);
 #endif
 };