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: I8e85af2a4e33836092816d38d9bbd7b43dd87d77

Android.bp

@@ -50,6 +50,7 @@ cc_library_static {
     name: "libc++_static",
     defaults: ["libc++ defaults"],
     vendor_available: true,
+    product_available: true,
     ramdisk_available: true,
     vendor_ramdisk_available: true,
     recovery_available: true,
@@ -109,6 +110,7 @@ cc_library_shared {
     name: "libc++",
     host_supported: true,
     vendor_available: true,
+    product_available: true,
     native_bridge_supported: true,
     vndk: {
         enabled: true,