Use 'private: true' for the LLDNK-private library

We used 'vendor_available: false' to define VNDK-private libraries.
However, 'vendor_available' is originally used to create vendor
variants that is available to vendor modules. To avoid the confusion
we are replacing it with 'private: true' for the private llndk.

Bug: 175768895
Test: build
Change-Id: Idf3fe054c59e019f9ed968ca5b6fe49ee6a5e0fc
1 file changed