clocksource/drivers/timer-riscv: Stop stimecmp when cpu hotplug

clocksource/drivers/timer-riscv: Stop stimecmp when cpu hotplug

Stop the timer when the cpu is going to be offline otherwise the
timer interrupt may be pending while performing power-down.

Suggested-by: Anup Patel <anup@brainfault.org>
Link: https://lore.kernel.org/lkml/20240829033904.477200-3-nick.hu@sifive.com/T/#u
Signed-off-by: Nick Hu <nick.hu@sifive.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20250219114135.27764-3-nick.hu@sifive.com
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>