drm_hwcomposer: Add support for virtual connectors

Allow virtual connector type in order to support virtio-gpu.

BUG=none
TEST=Tested with virtio-gpu on QEMU

Change-Id: I7ae5091d3587bcae75da6bff23d7bc85aa6164f1
Signed-off-by: Rob Herring <robh@kernel.org>
diff --git a/drmconnector.cpp b/drmconnector.cpp
index 7f1f2b0..8469c5e 100644
--- a/drmconnector.cpp
+++ b/drmconnector.cpp
@@ -69,7 +69,7 @@
 
 bool DrmConnector::built_in() const {
   return type_ == DRM_MODE_CONNECTOR_LVDS || type_ == DRM_MODE_CONNECTOR_eDP ||
-         type_ == DRM_MODE_CONNECTOR_DSI;
+         type_ == DRM_MODE_CONNECTOR_DSI || type_ == DRM_MODE_CONNECTOR_VIRTUAL;
 }
 
 int DrmConnector::UpdateModes() {