target/riscv: Enable/Disable S/VS-mode Timer when STCE bit is changed

target/riscv: Enable/Disable S/VS-mode Timer when STCE bit is changed

Updating STCE will enable/disable SSTC in S-mode or/and VS-mode, so we
also need to update S/VS-mode Timer and S/VSTIP bits in $mip CSR.

Signed-off-by: Jim Shu <jim.shu@sifive.com>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20250519143518.11086-5-jim.shu@sifive.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>