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: I75c5010d64151d873c76f48b497cdb71a09667e8
diff --git a/Android.bp b/Android.bp
index 29fda33..0e79125 100644
--- a/Android.bp
+++ b/Android.bp
@@ -13,6 +13,7 @@
     name: "libcap",
     host_supported: true,
     vendor_available: true,
+    product_available: true,
     recovery_available: true,
     vndk: {
         enabled: true,