Add missing hvdos public domain attribution:

hvf.c and vmx.h contain code from hvdos.c that is released as public domain:

from hvdos github: https://github.com/mist64/hvdos

"License

See LICENSE.txt (2-clause-BSD).

In order to simplify use of this code as a template, you can consider any parts from "hvdos.c" and "interface.h" as being in the public domain."

Signed-off-by: Izik Eidus <izik@veertu.com>
Message-Id: <20180123123639.35255-2-izik@veertu.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

target/i386/hvf/hvf.c

@@ -17,6 +17,9 @@
  *
  * You should have received a copy of the GNU Lesser General Public
  * License along with this program; if not, see <http://www.gnu.org/licenses/>.
+ *
+ * This file contain code under public domain from the hvdos project:
+ * https://github.com/mist64/hvdos
  */
 #include "qemu/osdep.h"
 #include "qemu-common.h"

target/i386/hvf/vmx.h

@@ -17,6 +17,9 @@
  *
  * You should have received a copy of the GNU Lesser General Public
  * License along with this program; if not, see <http://www.gnu.org/licenses/>.
+ *
+ * This file contain code under public domain from the hvdos project:
+ * https://github.com/mist64/hvdos
  */
 
 #ifndef VMX_H