mt/fesvr : Add FESVR support to cheshire

[mtravaillard]

This PR add support of FESVR and PK with slink as a preloading method.

• FESVR can now be used to run application using DMI interface, connected directly to the debug module.
• PK can be used to run apps in user space.
• It's possible to create baremetal apps that runs with FESVR, using riscv-tests repo (benchmark)
• SLINK is used to preload the first binary (pk or baremetal bin), making the simulation faster (2nd binary run over pk will be preloaded by FESVR)

There is a documentation in a new folder, to explain easily how to use the FESVR and other useful information.
To run a simulation, it's still done the same way but there is a different compilation script for the design, allowing to use FESVR.