arm64: dts: Add dts files for LG Electronics's lg1313 SoC

Add dtsi file to support lg1313 SoC which based on Cortex-A53.
Also add dts file to support lg1312 reference board which based
on lg1313 SoC.

Signed-off-by: Chanho Min <chanho.min@lge.com>
Signed-off-by: Olof Johansson <olof@lixom.net>