arch: Enable build with kvm feature

Currently `arch` crate cannot be built, by specifying `hypervisor/kvm`
to turn on the features required for its dependency - `hypervisor` crate
to build. Thus enabling `arch` crate to be built with command:

```sh
cargo build -p arch --features kvm
```

Signed-off-by: Ruoqing He <[email protected]>

arch/Cargo.toml

@@ -6,7 +6,7 @@ version = "0.1.0"
 
 [features]
 default = []
-kvm = []
+kvm = ["hypervisor/kvm"]
 sev_snp = []
 tdx = []