platform: Add OpenPiton platform support

OpenPiton is a research platform from Princeton University [1].

"OpenPiton is the world's first open source, general purpose,
multithreaded manycore processor. It is a tiled manycore
framework scalable from one to 1/2 billion cores."

Add OpenSBI support for OpenPiton. As it is based on ariane core,
it reuses the platform code from arine project.

[1]. https://github.com/PrincetonUniversity/openpiton



Signed-off-by: Atish Patra <atish.patra@wdc.com>
Reviewed-by: Anup Patel <anup.patel@wdc.com>