Revert "arm: Remove nsa310s board"

While this platform has not yet been converted, there is active efforts
to do so.  Keep the platform for now.

This reverts commit aa697e6904ba1b3144a46ec642d4695e7c0cdc3e.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/arch/arm/mach-kirkwood/Kconfig b/arch/arm/mach-kirkwood/Kconfig
index 8e343a5..cb4e9f2 100644
--- a/arch/arm/mach-kirkwood/Kconfig
+++ b/arch/arm/mach-kirkwood/Kconfig
@@ -53,6 +53,9 @@
 config TARGET_NAS220
 	bool "BlackArmor NAS220"
 
+config TARGET_NSA310S
+	bool "Zyxel NSA310S"
+
 config TARGET_SBx81LIFKW
 	bool "Allied Telesis SBx81GS24/SBx81GT40/SBx81XS6/SBx81XS16"
 
@@ -80,6 +83,7 @@
 source "board/Seagate/dockstar/Kconfig"
 source "board/Seagate/goflexhome/Kconfig"
 source "board/Seagate/nas220/Kconfig"
+source "board/zyxel/nsa310s/Kconfig"
 source "board/alliedtelesis/SBx81LIFKW/Kconfig"
 source "board/alliedtelesis/SBx81LIFXCAT/Kconfig"