Tell TF-A in EL3 about TEE message buffers.

This must be enabled by a flag in the manifest, as it won't work without
the matching support in TF-A, e.g. in the case of running tests on QEMU
without TF-A.

Bug: 132429380
Change-Id: I0a0848c7b1afb416d98c0afeabcc4601abf9d193
13 files changed