target/riscv: Add the checking into stimecmp write function.

target/riscv: Add the checking into stimecmp write function.

Preparation commit to let aclint timer to use stimecmp write function.
Aclint timer doesn't call sstc() predicate so we need to check inside
the stimecmp write function.

Signed-off-by: Jim Shu <jim.shu@sifive.com>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20250519143518.11086-2-jim.shu@sifive.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>