On ARM standard platforms, snoop and DVM requests used to be enabled
for the primary CPU's cluster only in the first EL3 bootloader.
In other words, if the platform reset into BL1 then CCI coherency
would be enabled by BL1 only, and not by BL3-1 again.

However, this doesn't cater for platforms that use BL3-1 along with
a non-TF ROM bootloader that doesn't enable snoop and DVM requests.
In this case, CCI coherency is never enabled.

This patch modifies the function bl31_early_platform_setup() on
ARM standard platforms so that it always enables snoop and DVM
requests regardless of whether earlier bootloader stages have
already done it. There is no harm in executing this code twice.

ARM Trusted Firmware Design document updated accordingly.

Change-Id: Idf1bdeb24d2e1947adfbb76a509f10beef224e1c

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