graphics: add HIDL definition for HW composer

This is a direct translation of hwcomposer2.h to HIDL.

Test: make
Change-Id: Id007af271b06f0d86afc8bc7c57300c588dc4081
diff --git a/Android.bp b/Android.bp
index 9098afc..d73f80b 100644
--- a/Android.bp
+++ b/Android.bp
@@ -7,6 +7,7 @@
     "biometrics/fingerprint/2.1",
     "graphics/allocator/2.0",
     "graphics/allocator/2.0/default",
+    "graphics/composer/2.1",
     "graphics/mapper/2.0",
     "graphics/mapper/2.0/default",
     "light/2.0",