Define POLICYVERS

Bug: 296875906
Bug: 289368466
Test: check kernel-sepolicy-version field in
  system/etc/vintf/compatibility_matrix.device.xml
Change-Id: I9b769db3649885a7b602c8ce9351b86472c84936
diff --git a/compatibility_matrices/Android.mk b/compatibility_matrices/Android.mk
index a82a421..d356cf3 100644
--- a/compatibility_matrices/Android.mk
+++ b/compatibility_matrices/Android.mk
@@ -56,6 +56,9 @@
 
 endif # DEVICE_FRAMEWORK_COMPATIBILITY_MATRIX_FILE
 
+# TODO(b/296875906): use POLICYVERS from Soong
+POLICYVERS ?= 30
+
 LOCAL_ADD_VBMETA_VERSION := true
 LOCAL_ASSEMBLE_VINTF_ENV_VARS := \
     POLICYVERS \