virtio-gpu: don't clear QemuUIInfo information on reset

Don't reset window layout information (passed via virtio_gpu_ui_info) on
device reset, so the user interface window layout will be kept intact
over reboots.  The head size and position was commented out already, so
this patch just drops the dead code.  Additionally the enabled head mask
must be kept so multihead setups work properly too.

Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1460595
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-id: 20170906142058.2460-1-kraxel@redhat.com
