plat/arm: Introduce TC0 platform

This patch adds support for Total Compute (TC0) platform. It is an
initial port and additional features are expected to be added later.

TC0 has a SCP which brings the primary Cortex-A out of reset
which starts executing BL1. TF-A optionally authenticates the SCP
ram-fw available in FIP and makes it available for SCP to copy.

Some of the major features included and tested in this platform
port include TBBR, PSCI, MHUv2 and DVFS.

Change-Id: I1675e9d200ca7687c215009eef483d9b3ee764ef
Signed-off-by: Usama Arif <usama.arif@arm.com>
diff --git a/docs/plat/arm/tc0/index.rst b/docs/plat/arm/tc0/index.rst
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+TC0 Total Compute Platform
+==========================
+
+Some of the features of TC0 platform referenced in TF-A include:
+
+- A `System Control Processor <https://github.com/ARM-software/SCP-firmware>`_
+  to abstract power and system management tasks away from application
+  processors. The RAM firmware for SCP is included in the TF-A FIP and is
+  loaded by AP BL2 from FIP in flash to SRAM for copying by SCP (SCP has access
+  to AP SRAM).
+- GICv4
+- Trusted Board Boot
+- SCMI
+- MHUv2
+
+Boot Sequence
+-------------
+
+The execution begins from SCP_BL1. SCP_BL1 powers up the AP which starts
+executing AP_BL1 and then executes AP_BL2 which loads the SCP_BL2 from
+FIP to SRAM. The SCP has access to AP SRAM. The address and size of SCP_BL2
+is communicated to SCP using SDS. SCP copies SCP_BL2 from SRAM to its own
+RAM and starts executing it. The AP then continues executing the rest of TF-A
+stages including BL31 runtime stage and hands off executing to
+Non-secure world (u-boot).
+
+Build Procedure (TF-A only)
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+-  Obtain arm `toolchain <https://developer.arm.com/tools-and-software/open-source-software/developer-tools/gnu-toolchain/gnu-a/downloads>`_.
+   Set the CROSS_COMPILE environment variable to point to the toolchain folder.
+
+-  Build TF-A:
+
+   .. code:: shell
+
+      make PLAT=tc0 BL33=<path_to_uboot.bin> \
+      SCP_BL2=<path_to_scp_ramfw.bin>  all fip
+
+   Enable TBBR by adding the following options to the make command:
+
+   .. code:: shell
+
+      MBEDTLS_DIR=<path_to_mbedtls_directory>  \
+      TRUSTED_BOARD_BOOT=1 \
+      GENERATE_COT=1 \
+      ARM_ROTPK_LOCATION=devel_rsa  \
+      ROT_KEY=plat/arm/board/common/rotpk/arm_rotprivk_rsa.pem
+
+*Copyright (c) 2020, Arm Limited. All rights reserved.*