[BUG] mstatush is not implemented in RV32

Created by: ASintzoff

Is there an existing CVA6 bug for this?

• I have searched the existing bug issues

Bug Description

The mstatush CSR which contains the 32 most significant bits of mstatus CSR in RV32 is not implemented.

For more details, see The RISC-V Instruction Set Manual Volume II: Privileged Architecture, section 3.1.6 - Machine Status Registers (mstatus and mstatush).