target/riscv: Trap on writes to stimecmp from VS when hvictl.VTI=1

target/riscv: Trap on writes to stimecmp from VS when hvictl.VTI=1

Per the AIA specification, writes to stimecmp from VS level should
trap when hvictl.VTI is set since the write may cause vsip.STIP to
become unset.

Fixes: 3ec0fe18a31f ("target/riscv: Add vstimecmp support")
Signed-off-by: Andrew Bresticker <abrestic@rivosinc.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20221215224541.1423431-2-abrestic@rivosinc.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>