[ARM] Orion: rework MPP handling

Instead of having board code poke directly into the MPP configuration
registers, and separately calling orion5x_gpio_set_valid_pins() to
indicate which MPP pins can be used as GPIO pins, introduce a helper
function for configuring the roles of each of the MPP pins, and have
that helper function handle gpio validity internally.

Signed-off-by: Lennert Buytenhek <buytenh@marvell.com>
Acked-by: Sylver Bruneau <sylver.bruneau@googlemail.com>
Acked-by: Russell King <linux@arm.linux.org.uk>
diff --git a/arch/arm/mach-orion5x/gpio.c b/arch/arm/mach-orion5x/gpio.c
index 8108c31..9fba6a1 100644
--- a/arch/arm/mach-orion5x/gpio.c
+++ b/arch/arm/mach-orion5x/gpio.c
@@ -24,9 +24,12 @@
 static unsigned long gpio_valid[BITS_TO_LONGS(GPIO_MAX)];
 static const char *gpio_label[GPIO_MAX];  /* non null for allocated GPIOs */
 
-void __init orion5x_gpio_set_valid_pins(u32 pins)
+void __init orion5x_gpio_set_valid(unsigned pin, int valid)
 {
-	gpio_valid[0] = pins;
+	if (valid)
+		__set_bit(pin, gpio_valid);
+	else
+		__clear_bit(pin, gpio_valid);
 }
 
 /*