rust: Add RISCV CSR registers

[Kritzefitz]

The addition of these registers in the C base caused the rust values
for all floating point registers and the PC to point to some of the
CSR registers instead.

[wtdcode]

Why not add the variables after PC=65?

[Kritzefitz]

The conversion of RegisterRISCV in rust to uc_riscv_reg in C goes via an intermediate int. This means the conversion of PC should looks something like this:

RegisterRISCV::PC -> 190 -> UC_RISCV_REG_PC

However, this assumes that the mapping between RegisterRISCV and ints int rust (which is defined explicitly) matches that between uc_riscv_reg and ints in C (which is implicitly defined by the order of the enum). When the CSR registers were added to uc_riscv_reg the mapping in C became out of sync with the mapping in rust, so the conversion of PC from rust to C currently looks something like this:

RegisterRISCV::PC -> 65 -> UC_RISCV_REG_HPMCOUNTER21

As you see, the C side thinks we want to read HPMCOUNTER21, when we actually want to read the PC. This is obviously not good.

To fix this, we need to change the mappings in rust for all registers that have been shifted by the addition of the CSR registers in the C code.

As a side note: keeping the mappings between registers in C and rust synced by hand seems pretty error prone to me. Unfortunately I don't know a better alternative, because rust's FFI to my knowledge doesn't provide a mechanism to access definitions of enums in C.

[wtdcode]

Sorry I realize it's my mistake here. The variables are in the right place.

[wtdcode]

Merged, thanks.