Build product hashes together.

Simplifies our reasoning about product hashes. They are either
present on both sides of the Treble boundary or not.

Might be worth installing all four hashes unconditionally in the future.

Fixes: 123996710
Test: boot taimen, precompiled policy loaded
Change-Id: I749e4b0cc4c85870407a10b7d41a2e2001a75ffb
diff --git a/Android.mk b/Android.mk
index 5f59e19..bb6cb53 100644
--- a/Android.mk
+++ b/Android.mk
@@ -264,6 +264,7 @@
     precompiled_sepolicy \
     precompiled_sepolicy.plat_sepolicy_and_mapping.sha256 \
     precompiled_sepolicy.product_sepolicy_and_mapping.sha256 \
+    product_sepolicy_and_mapping.sha256 \
 
 endif # ($(PRODUCT_PRECOMPILED_SEPOLICY),false)
 
@@ -303,7 +304,6 @@
     product_service_contexts \
     product_mac_permissions.xml \
     product_mapping_file \
-    product_sepolicy_and_mapping.sha256 \
 
 endif