arm: dts: Add base dtsi and devkit dts for Intel N5X device

Add device tree for N5X.

Signed-off-by: Siew Chin Lim <elly.siew.chin.lim@intel.com>
Signed-off-by: Tien Fong Chee <tien.fong.chee@intel.com>
Reviewed-by: Ley Foon Tan <lftan.linux@gmail.com>