gpio: do not include <asm/arch/gpio.h> on ARCH_BCM6858

As no gpio.h is defined for this architecture, to avoid
compilation failure, do not include <asm/arch/gpio.h> for
arch bcm6858.

Signed-off-by: Philippe Reynes <philippe.reynes@softathome.com>
diff --git a/arch/arm/include/asm/gpio.h b/arch/arm/include/asm/gpio.h
index 3039e66..15bd40f 100644
--- a/arch/arm/include/asm/gpio.h
+++ b/arch/arm/include/asm/gpio.h
@@ -1,5 +1,5 @@
 #if !defined(CONFIG_ARCH_UNIPHIER) && !defined(CONFIG_ARCH_STI) && \
-	!defined(CONFIG_ARCH_K3)
+	!defined(CONFIG_ARCH_K3) && !defined(CONFIG_ARCH_BCM6858)
 #include <asm/arch/gpio.h>
 #endif
 #include <asm-generic/gpio.h>