target/riscv: enable riscv kvm accel

target/riscv: enable riscv kvm accel

Add riscv kvm support in meson.build file.

Signed-off-by: Yifei Jiang <jiangyifei@huawei.com>
Signed-off-by: Mingwang Li <limingwang@huawei.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Message-id: 20220112081329.1835-14-jiangyifei@huawei.com
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>