Split libdvr_headers from libdvr: Step 1

Converts libdvr's Android file into Android.bp as now we have no Java
deps anymore. Then we added header only library libdvr_headers for all
headers.

Next step is to figure out how to split out public headers and make them
easy to be copied into Google3.

Bug: 37578558
Test: dvr_api-test
Change-Id: Idf15cfd5aa61cd7d6f5cc15c4db7cce485b3b293