Enable gofmt in preupload hooks

Test: none
Change-Id: I6a2e65efc84969058f8a540bdc4d0e8d4e661c9d

Author: colincross

PREUPLOAD.cfg

@@ -2,3 +2,6 @@
 whitespace = tools/whitespace.sh ${PREUPLOAD_FILES}
 aosp_hook = ${REPO_ROOT}/frameworks/base/tools/aosp/aosp_sha.sh ${PREUPLOAD_COMMIT} "."
 policy_version_check = tools/policy_version_check.sh
+
+[Builtin Hooks]
+gofmt = true