Initialize platform for MediaTek mt8192

- Add basic platform setup
- Add mt8192 documentation at docs/plat/
- Add generic CPU helper functions
- Add basic register address

Change-Id: Ife34622105404a8227441aab939e3c55c96374e9
diff --git a/docs/plat/mt8192.rst b/docs/plat/mt8192.rst
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+MediaTek 8192
+=============
+
+MediaTek 8192 (MT8192) is a 64-bit ARM SoC introduced by MediaTek in 2020.
+The chip incorporates eight cores - four Cortex-A55 little cores and Cortex-A76.
+Cortex-A76 can operate at up to 2.2 GHz.
+Cortex-A55 can operate at up to 2 GHz.
+
+Boot Sequence
+-------------
+
+::
+
+    Boot Rom --> Coreboot --> TF-A BL31 --> Depthcharge --> Linux Kernel
+
+How to Build
+------------
+
+.. code:: shell
+
+    make CROSS_COMPILE=aarch64-linux-gnu- PLAT=mt8192 DEBUG=1 COREBOOT=1