add missing CSRs to RISCV arch spec

[lasseUrban]

Resolves issue CSR MSTATUS for RISCV architecture doens't work -> add it to the VirtualStruct #121

[PhilippvK]

@lasseUrban the current default architecture should be RV32IMACFD as RISCV is quite outdated and does not pass the RISC-V compliance tests.

Also, the CSR-handling should now be generated automatically using the M2-ISA-R tool, thus hard coding this shouldn’t be a necessity anymore. (@wysiwyng)

[wysiwyng]

as @PhilippvK mentioned this is probably best handled by M2-ISA-R. How it should be handled is open to discussion, I suggest shifting this to an issue in that repository.