arm: marvell: Extract kirkwood gpio functions into new common file gpio.c

This makes is possible to use those gpio functions from other MVEBU SoC's as well.

Signed-off-by: Stefan Roese <sr@denx.de>
Tested-by: Luka Perkov <luka@openwrt.org>
Acked-by: Prafulla Wadaskar <prafulla@marvell.com>
diff --git a/arch/arm/mvebu-common/Makefile b/arch/arm/mvebu-common/Makefile
index 391a125..9dcab69 100644
--- a/arch/arm/mvebu-common/Makefile
+++ b/arch/arm/mvebu-common/Makefile
@@ -7,5 +7,6 @@
 #
 
 obj-y	= dram.o
+obj-y	+= gpio.o
 obj-$(CONFIG_ARMADA_XP) += mbus.o
 obj-y	+= timer.o