feat(fvp): implement platform API for load and auth image

Introduce and implement a stub implementation of
`plat_lfa_load_auth_image()` for the FVP platform. For AEM FVP, no
actual image loading or authentication is required as of now, as
images are assumed to be pre-loaded and authenticated.

Signed-off-by: Manish V Badarkhe <Manish.Badarkhe@arm.com>
Change-Id: I82e51f5d18db6d5b9c61f9081b451619d761abe8
2 files changed