Platform,Silicon: import AMD Styx SoC support and platforms

Common files for AMD Overdrive, SoftIron Overdrive 1000
and LeMaker Cello, as well as actual platform support.
Imported from commit efd798c1eb of
https://git.linaro.org/uefi/OpenPlatformPkg.git



Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Leif Lindholm <leif.lindholm@linaro.org>