feat(measured boot): add documentation to build and run PoC

Add documentation to build and run a PoC based on the OP-TEE toolkit
to show how TF-A Measured Boot can interact with a third party (f)TPM
service.

Signed-off-by: Javier Almansa Sobrino <javier.almansasobrino@arm.com>
Change-Id: I11ac99c4ff54ea52aba0731aa7f707d7cd0c4216
2 files changed