spmd: Fix signedness comparison warning ...

With -Wsign-compare, compilers issue a warning in the SPMD code:
====================
services/std_svc/spmd/spmd_pm.c:35:22: error: comparison of integer
expressions of different signedness: 'int' and 'unsigned int'
[-Werror=sign-compare]
   35 |  if ((id < 0) || (id >= PLATFORM_CORE_COUNT)) {
      |                      ^~
cc1: all warnings being treated as errors
====================

Since we just established that "id" is positive, we can safely cast it
to an unsigned type to make the comparison have matching types.

Change-Id: I6ef24804c88136d7e3f15de008e4fea854f10ffe
Signed-off-by: Andre Przywara <andre.przywara@arm.com>

SPMC: embed secondary core ep info into to SPMC context ...

Signed-off-by: Olivier Deprez <olivier.deprez@arm.com>
Signed-off-by: Max Shvetsov <maksims.svecovs@arm.com>
Change-Id: Icdb15b8664fb3467ffd55b44d1f0660457192586

SPMD: secondary cores PM on and off SPD hooks relayed to SPMC ...

Define SPMD PM hooks for warm boot and off events. svc_on_finish handler
enters the SPMC at the entry point defined by the secondary EP register
service. The svc_off handler notifies the SPMC that a physical core is
being turned off through a notification message.

Signed-off-by: Olivier Deprez <olivier.deprez@arm.com>
Change-Id: I2609a75a0c6ffb9f6313fc09553be2b29a41de59

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

SPMD: add generic SPD PM handlers ...

This patch defines and registers the SPMD PM handler hooks.
This is intended to relay boot and PM events to the SPMC.

Change-Id: If5a758d22b8d2152cbbb83a0cad563b5e1c6bd49
Signed-off-by: Olivier Deprez <olivier.deprez@arm.com>
Signed-off-by: Max Shvetsov <maksims.svecovs@arm.com>