Experimental OpenSBI fork for trap-based ISA extension emulation

[Benedikt Freisen]

Good evening everyone!

With the European RISC-V Summit quickly approaching, I have decided to 
make my recent experiments involving trap-based emulation of ISA 
extensions relevant to RVA22, RVB23 and RVA23 publicly available.

Since they add quite a bit of code that would hardly be relevant to the 
average OpenSBI use case, I have uploaded everything as a fork on 
GitHub, named opensbi-isa-ext-emu*.

It currently fully emulates the ISA extensions Zba, Zbb, Zbs, Zfhmin, 
Zicond, Zimop, Zcmop, Zcb and Zfa, whereas the implementations of the 
cache-related extensions Zcbom, Zcboz and Zawrs are currently stubs.

Please be aware that this ISA extension emulation is highly experimental 
and expect bugs, because the code is still quite new and there has only 
been rudimentary testing in Qemu.

Your feedback and opinions are welcome.

Greetings,
Benedikt

*) https://github.com/roybaer/opensbi-isa-ext-emu