[virtio] Move virtio-pci.h and virtio-ring.h to include/gpxe

Signed-off-by: Laurent Vivier <Laurent.Vivier@bull.net>

src/drivers/net/virtio-net.c

 
 #include "etherboot.h"
 #include "nic.h"
-#include "virtio-ring.h"
-#include "virtio-pci.h"
+#include "gpxe/virtio-ring.h"
+#include "gpxe/virtio-pci.h"
 #include "virtio-net.h"
 
 #define BUG() do { \