init: use protobuf for serialization of persistent properties

I probably should have done this from the start...  There's a shim to
convert my manually serialized format to protobuf, and since that has
not yet shipped, it'll be reverted in a short period of time.

Test: init unit tests
Test: upgrade from legacy and intermediate property formats successfully
Change-Id: Iad25f6c30d0b44d294230a53dd6876222d1c785b
diff --git a/init/Android.mk b/init/Android.mk
index 6c28517..dd0f1bf 100644
--- a/init/Android.mk
+++ b/init/Android.mk
@@ -82,6 +82,7 @@
     libprocessgroup \
     libavb \
     libkeyutils \
+    libprotobuf-cpp-lite \
 
 LOCAL_REQUIRED_MODULES := \
     e2fsdroid \