Switch makefile owners to MK_OWNERS

Bug: 278167548
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:f7ac0c78286f5a93d0a894963fdb466fc225e438)
Merged-In: Iff0ba2691a738407a3bbb86a221b20314457db24
Change-Id: Iff0ba2691a738407a3bbb86a221b20314457db24

OWNERS

@@ -1,4 +1,4 @@
 per-file powerhint.json = [email protected],[email protected],[email protected],[email protected]
 
 # 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:main:/OWNERS
+per-file *.mk,*/BoardConfig.mk=file:device/google/gs-common:main:/MK_OWNERS