[ARM] Introduce common dtsi files for preconfigured guests

This patch reduces lot of redundancy among various DTS files of various ARM board supports by having dtsi files for preconfigured guests.

This is inspired from approach taken by Exynos4 board support to reduce redundanc among for SMDKC210 & NURI DTS files.

Signed-off-by: Anup Patel <anup@brainfault.org>