Add OWNERS in frameworks/av

* Owners are selected from top CL approvals or owners.
  They will be suggested to review/approve future CLs.
* OWNERS files are recognized by the new find-owners plugin, see .md files in
  https://gerrit.googlesource.com/plugins/find-owners/+/master/src/main/resources/Documentation/

Test: build/make/tools/checkowners.py -c -v OWNERS
Change-Id: I7c848855a2d7a0d7f33123ea4ef5c2d03977b495
diff --git a/OWNERS b/OWNERS
new file mode 100644
index 0000000..8f405e9
--- /dev/null
+++ b/OWNERS
@@ -0,0 +1,4 @@
+elaurent@google.com
+etalvala@google.com
+lajos@google.com
+marcone@google.com