build(app): add python scripts for El0 apps

Add python scripts for creating final RMM image file with apps boundled
to it.

* app/gen_app_bin.py is for generating bin file from an app elf file.
  This bin can be bundled with an RMM bin file
* app/bundle_app_rmm.py is for creating a bundle from an RMM bin image,
  and 1 or more app bin files.

Change-Id: I209d6869370659a764b2849d45bb6b147c484e7d
Signed-off-by: Mate Toth-Pal <mate.toth-pal@arm.com>
4 files changed