Add product_available to product available modules

vendor_available modules were available to product modules.
However, not all vendor_available modules are required to be
available to product modules. Some modules want to be available only
to product modules but not vendor modules.

To cover the requirement, we separate product_available from
vendor_available.
vendor_available will not provide product available module.

Bug: 150902910
Test: build
Change-Id: I3fea06067f4b085af5fa981ac60958fc3bd4b045
diff --git a/Android.bp b/Android.bp
index 2593715..034919e 100644
--- a/Android.bp
+++ b/Android.bp
@@ -69,6 +69,7 @@
     native_bridge_supported: true,
     recovery_available: true,
     vendor_available: true,
+    product_available: true,
     apex_available: [
         // TODO(b/137948090): not fully supported in APEX for certain usecases
         // - large dependency sizes