drm_hwcomposer: Add composition skipping backend

This display backend may be chosen by setting the hwc.backend_override
system property to the "client" value.

Suggested-by: Andrii Chepurnyi <andrii_chepurnyi@epam.com>
Signed-off-by: Matvii Zorin <matvii.zorin@globallogic.com>
diff --git a/Android.bp b/Android.bp
index b4bf8e0..e6b767e 100644
--- a/Android.bp
+++ b/Android.bp
@@ -97,6 +97,7 @@
 
         "backend/backendmanager.cpp",
         "backend/backend.cpp",
+        "backend/backendclient.cpp",
     ],
 }