Refactor LOCAL_INIT_RC

We supported de-duplicating LOCAL_INIT_RC across multiple architecture
variants in a single module definition, but that didn't work if the
module was defined with two different BUILD_PREBUILT definitions. That's
how we're exporting modules from Soong to Make.

Change-Id: Ifc93b15ef78ea3d8e78005d428a3ec57d7e414e8