[MIPS] make fallback gpio.h gpiolib-friendly

If gpiolib was selected, asm-generic/gpio.h provides some prototypes
for gpio API and implementation helpers.  With this patch, platform
code can implement its GPIO API using gpiolib without custom gpio.h
file.
Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

include/asm-mips/mach-generic/gpio.h

 #ifndef __ASM_MACH_GENERIC_GPIO_H
 #define __ASM_MACH_GENERIC_GPIO_H
 
+#ifdef CONFIG_HAVE_GPIO_LIB
+#define gpio_get_value	__gpio_get_value
+#define gpio_set_value	__gpio_set_value
+#define gpio_cansleep	__gpio_cansleep
+#else
 int gpio_request(unsigned gpio, const char *label);
 void gpio_free(unsigned gpio);
 int gpio_direction_input(unsigned gpio);
 int gpio_direction_output(unsigned gpio, int value);
 int gpio_get_value(unsigned gpio);
 void gpio_set_value(unsigned gpio, int value);
+#endif
 int gpio_to_irq(unsigned gpio);
 int irq_to_gpio(unsigned irq);