refactor(app): add API to access mapped RMM app heap

This commit updates the RMM app framework API, so that an app
implementation's rmm_stub can access the EL0 heap.

Change-Id: Ie938fa07cf6f3325fc2d7509b3e8d908ef6a17e8
Signed-off-by: Mate Toth-Pal <mate.toth-pal@arm.com>
12 files changed