gralloc: create a common gralloc interface

Create gralloc interface for allocator and mapper to hide the
implementation differences between Gralloc2 and Gralloc3.

Bug: 120493579
Test: manual
Change-Id: I21aa1954aa8b79f3e35616f188e15b47dae1f0e7
diff --git a/libs/ui/Android.bp b/libs/ui/Android.bp
index 956465c..84414e2 100644
--- a/libs/ui/Android.bp
+++ b/libs/ui/Android.bp
@@ -60,6 +60,7 @@
         "Fence.cpp",
         "FenceTime.cpp",
         "FrameStats.cpp",
+        "Gralloc.cpp",
         "Gralloc2.cpp",
         "GraphicBuffer.cpp",
         "GraphicBufferAllocator.cpp",