target/riscv: Add select value range check for counter delegation

target/riscv: Add select value range check for counter delegation

This adds checks in ops performed on xireg and xireg2-xireg6 so that the
counter delegation function will receive a valid xiselect value with the
proper extensions enabled.

Co-developed-by: Atish Patra <atishp@rivosinc.com>
Signed-off-by: Kaiwen Xue <kaiwenx@rivosinc.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Atish Patra <atishp@rivosinc.com>
Message-ID: <20250110-counter_delegation-v5-7-e83d797ae294@rivosinc.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>