Add interface tag

so other components can start the hal interface when needed.

Test: manual
Change-Id: I61a4d396e86ec8dbda2cbabcc7afca7be7628f26
(cherry picked from commit c4f493977b6315d3dfe8e05f0c2516e2b00feca4)
diff --git a/graphics/allocator/2.0/default/android.hardware.graphics.allocator@2.0-service.rc b/graphics/allocator/2.0/default/android.hardware.graphics.allocator@2.0-service.rc
index 6eee71f..a2a881a 100644
--- a/graphics/allocator/2.0/default/android.hardware.graphics.allocator@2.0-service.rc
+++ b/graphics/allocator/2.0/default/android.hardware.graphics.allocator@2.0-service.rc
@@ -1,5 +1,6 @@
 service vendor.gralloc-2-0 /vendor/bin/hw/android.hardware.graphics.allocator@2.0-service
     class hal animation
+    interface android.hardware.graphics.allocator@2.0::IAllocator default
     user system
     group graphics drmrpc
     capabilities SYS_NICE