feat(spmd): enable handling of FF-A SMCs with the SPMC at EL3

feat(spmd): enable handling of FF-A SMCs with the SPMC at EL3

Any FF-A SMC that arrives from the normal world is handled by the
SPMD before being forwarded to the SPMC. Similarly any SMC
arriving from the secure world will hit the SPMC first and be
forwarded to the SPMD if required, otherwise the SPMC will
respond directly.

This allows for the existing flow of handling FF-A ABI's when
the SPMC resides at a lower EL to be preserved.

In order to facilitate this flow the spmd_smc_forward function
has been split and control is either passed to the SPMC or it is
forwarded as before. To allow this the flags and cookie parameters
must now also be passed into this method as the SPMC must be able to
provide these when calling back into the SPMD handler as appropriate.

Signed-off-by: Marc Bonnici <marc.bonnici@arm.com>
Change-Id: I84fee8390023295b9689067e14cd25cba23ca39b