ARM: S5PC1xx: add gpiolib and external/gpio interrupt support

Add support for gpiolib calls. This is based on the gpiolib implementation
from plat-s3c64xx tree.
Add support for external interrupts for GPIO H banks.
Add support for GPIO interrupts for all banks.

Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>
diff --git a/arch/arm/plat-s5pc1xx/irq.c b/arch/arm/plat-s5pc1xx/irq.c
index 80d6dd9..e44fd04 100644
--- a/arch/arm/plat-s5pc1xx/irq.c
+++ b/arch/arm/plat-s5pc1xx/irq.c
@@ -79,7 +79,7 @@
 {
 	u32 reg = __raw_readl(S3C64XX_TINT_CSTAT);
 
-	reg &= 0x1f;
+	reg &= 0x1f;  /* mask out pending interrupts */
 	reg |= (1 << 5) << (irq - IRQ_TIMER0);
 	__raw_writel(reg, S3C64XX_TINT_CSTAT);
 }