x86/gpio: Implement x86 gpio_to_irq convert function

We need this for x86 MID platforms where GPIO interrupts are
used. No special magic is needed so the default 1:1 behaviour
will do nicely.
Signed-off-by: NAlek Du <alek.du@intel.com>
Signed-off-by: NJacob Pan <jacob.jun.pan@intel.com>
Signed-off-by: NAlan Cox <alan@linux.intel.com>
LKML-Reference: <20110111105439.24448.69863.stgit@bob.linux.org.uk>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

arch/x86/include/asm/gpio.h

@@ -38,12 +38,9 @@ static inline int gpio_cansleep(unsigned int gpio)
 	return __gpio_cansleep(gpio);
 }
 
-/*
- * Not implemented, yet.
- */
 static inline int gpio_to_irq(unsigned int gpio)
 {
-	return -ENOSYS;
+	return __gpio_to_irq(gpio);
 }
 
 static inline int irq_to_gpio(unsigned int irq)