Attest: Add IPC compatibility

1. Add IPC implementation for both secure and non-secure Initial
   Attestation APIs.
2. Update Initial Attestation Service manifest to support IPC model.
3. Add thread like behaviour to receive and handle requests according
   to IPC model.

Change-Id: Ia27a9e9661ed716bc7eb84d6f077252e0319a586
Signed-off-by: Kevin Peng <kevin.peng@arm.com>
Co-authored-by: Moran Peker <moran.peker@arm.com>