target/riscv: Implement virtual time adjusting with vm state changing

target/riscv: Implement virtual time adjusting with vm state changing

We hope that virtual time adjusts with vm state changing. When a vm
is stopped, guest virtual time should stop counting and kvm_timer
should be stopped. When the vm is resumed, guest virtual time should
continue to count and kvm_timer should be restored.

Signed-off-by: Yifei Jiang <jiangyifei@huawei.com>
Signed-off-by: Mingwang Li <limingwang@huawei.com>
Reviewed-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-id: 20220112081329.1835-12-jiangyifei@huawei.com
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>