ARM: OMAP: Add comment on why omap_gpio_init() is needed on some boards

Add comment on why omap_gpio_init() is needed on some boards

arch/arm/plat-omap/gpio.c

@@ -1051,6 +1051,7 @@ static struct sys_device omap_gpio_device = {
 
 /*
  * This may get called early from board specific init
+ * for boards that have interrupts routed via FPGA.
  */
 int omap_gpio_init(void)
 {