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/index.rst b/docs/plat/index.rst
index 7969003..6a38113 100644
--- a/docs/plat/index.rst
+++ b/docs/plat/index.rst
@@ -19,6 +19,7 @@
    intel-stratix10
    marvell/index
    mt8183
+   mt8192
    nvidia-tegra
    warp7
    imx8