cargo: Bump the kvm and vmm-sys-util crates

Since the kvm crates now depend on vmm-sys-util, the bump must be
atomic.
The kvm-bindings and ioctls 0.2.0 and 0.4.0 crates come with a few API
changes, one of them being the use of a kvm_ioctls specific error type.
Porting our code to that type makes for a fairly large diff stat.

Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

Cargo.toml

@@ -20,7 +20,7 @@ virtio-bindings = "0.1.0"
 vmm = { path = "vmm" }
 vm-device = { path = "vm-device" }
 vm-memory = { git = "https://github.com/rust-vmm/vm-memory" }
-vmm-sys-util = ">=0.1.1"
+vmm-sys-util = ">=0.2.1"
 vm-virtio = { path = "vm-virtio" }
 
 [dev-dependencies]