arm: add basic support for Mediatek MT6589 boards

This adds a generic devicetree board file and a dtsi for boards
based on MT6589 SoCs from Mediatek.

Apart from the generic parts (gic, clocks) the only component
currently supported are the timers.

Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 87b63fd..845c12d 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -978,6 +978,8 @@
 
 source "arch/arm/mach-imx/Kconfig"
 
+source "arch/arm/mach-mediatek/Kconfig"
+
 source "arch/arm/mach-mxs/Kconfig"
 
 source "arch/arm/mach-netx/Kconfig"