As a follow-up to bdd2596d4, and related to SPM Dispatcher
EL3 component and SPM Core S-EL2/S-EL1 component: update
with cosmetic and coding rules changes. In addition:
-Add Armv8.4-SecEL2 arch detection helper.
-Add an SPMC context (on current core) get helper.
-Return more meaningful error return codes.
-Remove complexity in few spmd_smc_handler switch-cases.
-Remove unused defines and structures from spmd_private.h

Signed-off-by: Olivier Deprez <olivier.deprez@arm.com>
Change-Id: I99e642450b0dafb19d3218a2f0e2d3107e8ca3fe