[CORE] First-cut implementation of SMP IPI APIs

This patch adds first working version of IPI APIs for SMP systems.

For now, we have following APIs:
1. Asynchronous call to a function on multiple processors
2. Synchronous call to a function on multiple processors

In future, this APIs will be improved and enriched as needed.

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