[PATCH v2 6/6] xactengine3_7: Implement IXACT3Engine::RegisterNotification and IXACT3Engine::UnRegisterNotification functions.

[Vijay Kiran Kamuju]

Based on patches from Ethan Lee and Alistair Leslie-Hughes.

Signed-off-by: Vijay Kiran Kamuju <infyquest(a)gmail.com>