target/riscv: Enforce WARL behavior for scounteren/hcounteren

target/riscv: Enforce WARL behavior for scounteren/hcounteren

scounteren/hcountern are also WARL registers similar to mcountern.
Only set the bits for the available counters during the write to
preserve the WARL behavior.

Signed-off-by: Atish Patra <atishp@rivosinc.com>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20240711-smcntrpmf_v7-v8-9-b7c38ae7b263@rivosinc.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>