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 will not provide product available module.

Bug: 150902910
Test: build
Change-Id: I045429f8d46ea443c4393dc858c8ee87ee3d339a
diff --git a/Android.bp b/Android.bp
index 749de15..b97ee0d 100644
--- a/Android.bp
+++ b/Android.bp
@@ -54,6 +54,7 @@
     name: "libunwind_llvm",
     sdk_version: "21",
     vendor_available: true,
+    product_available: true,
     ramdisk_available: true,
     vendor_ramdisk_available: true,
     recovery_available: true,