Refactor OWNERS files in platform/build/make.

Pulls out all of the per-file rules into their relevant directories
and includes platform/build/soong:/OWNERS as the authoritative
list of approvers.

Test: treehugger
Bug: 170407947
Change-Id: Icb885fc25a638f2f5134f6223df656ef4438bb67
diff --git a/core/OWNERS b/core/OWNERS
index 459683e..5456d4f 100644
--- a/core/OWNERS
+++ b/core/OWNERS
@@ -1,2 +1,6 @@
 per-file dex_preopt*.mk = ngeoffray@google.com,calin@google.com,mathewi@google.com,dbrazdil@google.com
 per-file verify_uses_libraries.sh = ngeoffray@google.com,calin@google.com,mathieuc@google.com
+
+# For version updates
+per-file version_defaults.mk = aseaton@google.com,elisapascual@google.com,lubomir@google.com,pscovanner@google.com
+