bootindex: support to set a existent device's bootindex to -1

When set a device's bootindex to -1, we remove it from global
fw_boot_order list.
Signed-off-by: NGonglei <arei.gonglei@huawei.com>
Reviewed-by: NGerd Hoffmann <kraxel@redhat.com>
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

bootdevice.c

@@ -77,6 +77,7 @@ void add_boot_device_path(int32_t bootindex, DeviceState *dev,
     FWBootEntry *node, *i;
 
     if (bootindex < 0) {
+        del_boot_device_path(dev, suffix);
         return;
     }