rust: qom: move device_id to PL011 class side

rust: qom: move device_id to PL011 class side

There is no need to monkeypatch DeviceId::Luminary into the already-initialized
PL011State.  Instead, now that we can define a class hierarchy, we can define
PL011Class and make device_id a field in there.

There is also no need anymore to have "Arm" as zero, so change DeviceId into a
wrapper for the array; all it does is provide an Index<hwaddr> implementation
because arrays can only be indexed by usize.

Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>