graphics: add a default implementation to IAllocator

The default implementatoin is built on top of conventional gralloc1.

This also adds a static library, libgralloc1-adapter.  It is intended to
ease the porting of gralloc0 to gralloc1.

Test: booted to launcher, tested with YouTube and some games.

Change-Id: Id640b1d5a1e1eea1aafabb6c134e6be6e71afff5
diff --git a/Android.bp b/Android.bp
index 727054c..6f85a70 100644
--- a/Android.bp
+++ b/Android.bp
@@ -4,6 +4,7 @@
     "audio/effect/2.0",
     "benchmarks/msgq/1.0",
     "graphics/allocator/2.0",
+    "graphics/allocator/2.0/default",
     "memtrack/1.0",
     "memtrack/1.0/default",
     "nfc/1.0",