target/riscv: Support start kernel directly by KVM

target/riscv: Support start kernel directly by KVM

Get kernel and fdt start address in virt.c, and pass them to KVM
when cpu reset. Add kvm_riscv.h to place riscv specific interface.

In addition, PLIC is created without M-mode PLIC contexts when KVM
is enabled.

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: 20220112081329.1835-7-jiangyifei@huawei.com
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>