This patch adds the capability to power down at system power domain level
on Juno via the PSCI SYSTEM SUSPEND API. The CSS power management helpers
are modified to add support for power management operations at system
power domain level. A new helper for populating `get_sys_suspend_power_state`
handler in plat_psci_ops is defined. On entering the system suspend state,
the SCP powers down the SYSTOP power domain on the SoC and puts the memory
into retention mode. On wakeup from the power down, the system components
on the CSS will be reinitialized by the platform layer and the PSCI client
is responsible for restoring the context of these system components.

According to PSCI Specification, interrupts targeted to cores in PSCI CPU
SUSPEND should be able to resume it. On Juno, when the system power domain
is suspended, the GIC is also powered down. The SCP resumes the final core
to be suspend when an external wake-up event is received. But the other
cores cannot be woken up by a targeted interrupt, because GIC doesn't
forward these interrupts to the SCP. Due to this hardware limitation,
we down-grade PSCI CPU SUSPEND requests targeted to the system power domain
level to cluster power domain level in `juno_validate_power_state()`
and the CSS default `plat_arm_psci_ops` is overridden in juno_pm.c.

A system power domain resume helper `arm_system_pwr_domain_resume()` is
defined for ARM standard platforms which resumes/re-initializes the
system components on wakeup from system suspend. The security setup also
needs to be done on resume from system suspend, which means
`plat_arm_security_setup()` must now be included in the BL3-1 image in
addition to previous BL images if system suspend need to be supported.

Change-Id: Ie293f75f09bad24223af47ab6c6e1268f77bcc47

Now that the FVP mailbox is no longer zeroed, the function
platform_mem_init() does nothing both on FVP and on Juno. Therefore,
this patch pools it as the default implementation on ARM platforms.

Change-Id: I007220f4531f15e8b602c3368a1129a5e3a38d91

This patch migrates ARM reference platforms, Juno and FVP, to the new platform
API mandated by the new PSCI power domain topology and composite power state
frameworks. The platform specific makefiles now exports the build flag
ENABLE_PLAT_COMPAT=0 to disable the platform compatibility layer.

Change-Id: I3040ed7cce446fc66facaee9c67cb54a8cd7ca29

This major change pulls out the common functionality from the
FVP and Juno platform ports into the following categories:

*   (include/)plat/common. Common platform porting functionality that
typically may be used by all platforms.

*   (include/)plat/arm/common. Common platform porting functionality
that may be used by all ARM standard platforms. This includes all
ARM development platforms like FVP and Juno but may also include
non-ARM-owned platforms.

*   (include/)plat/arm/board/common. Common platform porting
functionality for ARM development platforms at the board
(off SoC) level.

*   (include/)plat/arm/css/common. Common platform porting
functionality at the ARM Compute SubSystem (CSS) level. Juno
is an example of a CSS-based platform.

*   (include/)plat/arm/soc/common. Common platform porting
functionality at the ARM SoC level, which is not already defined
at the ARM CSS level.

No guarantees are made about the backward compatibility of
functionality provided in (include/)plat/arm.

Also remove any unnecessary variation between the ARM development
platform ports, including:

*   Unify the way BL2 passes `bl31_params_t` to BL3-1. Use the
Juno implementation, which copies the information from BL2 memory
instead of expecting it to persist in shared memory.

*   Unify the TZC configuration. There is no need to add a region
for SCP in Juno; it's enough to simply not allow any access to
this reserved region. Also set region 0 to provide no access by
default instead of assuming this is the case.

*   Unify the number of memory map regions required for ARM
development platforms, although the actual ranges mapped for each
platform may be different. For the FVP port, this reduces the
mapped peripheral address space.

These latter changes will only be observed when the platform ports
are migrated to use the new common platform code in subsequent
patches.

Change-Id: Id9c269dd3dc6e74533d0e5116fdd826d53946dc8