Add device mk OWNERS

Bug: 278167548
Change-Id: I4cb78bbb94fcfda984433636b24c95e7440297f2

OWNERS

@@ -1 +1,4 @@
 per-file powerhint.json = jychen@google.com,jenhaochen@google.com,wvw@google.com,joaodias@google.com
+
+# per-file for Pixel device makefiles, see go/pixel-device-mk-owner-checklist for details.
+per-file *.mk,*/BoardConfig.mk=file:device/google/gs-common:master:/OWNERS