[LIBS] Add red black tree APIs

Balanced binary tree (or Red Black tree) can be very useful in
implementing O(log n) in all parts of Xvisor where we can represent
data as binary search tree.
(Refer, http://en.wikipedia.org/wiki/Rbtree)

This patch ports linux red black tree APIs to libs/common.

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