target/riscv: Add kvm_riscv_get/put_regs_timer

target/riscv: Add kvm_riscv_get/put_regs_timer

Add kvm_riscv_get/put_regs_timer to synchronize virtual time context
from KVM.

To set register of RISCV_TIMER_REG(state) will occur a error from KVM
on kvm_timer_state == 0. It's better to adapt in KVM, but it doesn't matter
that adaping in QEMU.

Signed-off-by: Yifei Jiang <jiangyifei@huawei.com>
Signed-off-by: Mingwang Li <limingwang@huawei.com>
Reviewed-by: Anup Patel <anup.patel@wdc.com>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Message-id: 20220112081329.1835-11-jiangyifei@huawei.com
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>