Add initial support of riscv64

[liulog]

Due to lack of riscv support in some crates, I just use patch to reference my repo (forked from original repo).

[patch.crates-io]
axvmconfig = {git = "https://github.com/liulog/axvmconfig.git", branch = "next"}
axvisor_api = {git = "https://github.com/liulog/axvisor_api.git", branch = "master"}
riscv_vcpu = {git= "https://github.com/liulog/riscv_vcpu.git", branch = "master"}

[patch."https://github.com/arceos-hypervisor/axvm.git"]
axvm = {git="https://github.com/liulog/axvm.git", branch = "next"}

[patch."https://github.com/arceos-hypervisor/axdevice.git"]
axdevice = {git="https://github.com/liulog/axdevice.git", branch = "master"}

Related PRs aren't merged yet, you can use this.

Note:
For current axvisor, linux should config CONFIG_RISCV_SBI_V01=y.

My develop logging is recorded in #303.

[liulog]

You can quickly test it.

But before merged, I need submit PR about related patches mentioned above.

[ZR233]

riscv_vplic 可以PR到这个仓库，方便后续合作开发：https://github.com/arceos-hypervisor/riscv_vplic

[liulog]

riscv_vplic 可以PR到这个仓库，方便后续合作开发：https://github.com/arceos-hypervisor/riscv_vplic

好的，可能需要您这边对这个仓库进行一下初始化，当前仓库为空，无法 fork

[ZR233]

riscv_vplic 可以PR到这个仓库，方便后续合作开发：https://github.com/arceos-hypervisor/riscv_vplic

好的，可能需要您这边对这个仓库进行一下初始化，当前仓库为空，无法 fork

已授权，可直接操作