omap: define _toggle_gpio_edge_triggering only for OMAP1

The only usage of _toggle_gpio_edge_triggering is in
an #ifdef CONFIG_ARCH_OMAP1 block, so only provide it if
CONFIG_ARCH_OMAP1 is defined, too.

This fixes a compiler warning:

arch/arm/plat-omap/gpio.c:758: warning: '_toggle_gpio_edge_triggering' defined but not used

when compiling for ARCH_OMAP2, ARCH_OMAP3 or ARCH_OMAP4.

Signed-off-by: Uwe Kleine-König <[e-mail]>
Acked-by: Kevin Hilman <[e-mail]>
Signed-off-by: Tony Lindgren <[e-mail]>

arch/arm/plat-omap/gpio.c

···
 }
 #endif
 
+#ifdef CONFIG_ARCH_OMAP1
 /*
  * This only applies to chips that can't do both rising and falling edge
  * detection at once.  For all other chips, this function is a noop.
···
 	u32 l = 0;
 
 	switch (bank->method) {
-#ifdef CONFIG_ARCH_OMAP1
 	case METHOD_MPUIO:
 		reg += OMAP_MPUIO_GPIO_INT_EDGE;
 		break;
-#endif
 #ifdef CONFIG_ARCH_OMAP15XX
 	case METHOD_GPIO_1510:
 		reg += OMAP1510_GPIO_INT_CONTROL;
···
 
 	__raw_writel(l, reg);
 }
+#endif
 
 static int _set_gpio_triggering(struct gpio_bank *bank, int gpio, int trigger)
 {