SPMD: handle SPMC message to register secondary core entry point

SPMD: handle SPMC message to register secondary core entry point

Upon booting, the SPMC running on the primary core shall register the
secondary core entry points to which a given secondary core being woken
up shall jump to into the SPMC . The current implementation assumes the
SPMC calls a registering service implemented in the SPMD for each core
identified by its MPIDR. This can typically happen in a simple loop
implemented in the early SPMC initialization routines by passing each
core identifier associated with an entry point address and context
information.
This service is implemented on top of a more generic SPMC<=>SPMD
interface using direct request/response message passing as defined by
the FF-A specification.

Signed-off-by: Olivier Deprez <olivier.deprez@arm.com>
Signed-off-by: Max Shvetsov <maksims.svecovs@arm.com>
Change-Id: I1f70163b6b5cee0880bd2004e1fec41e3780ba35