vndk-def: Rename Indirect to Private

This commit adds LL-NDK-Private, VNDK-Private, and VNDK-SP-Private.

* LL-NDK-Private stands for the dependencies of LL-NDK shared libraries
  that must be inaccessible to vendor modules.

* VNDK-Private stands for the VNDK shared libraries that can be used by
  other VNDK shared libraries but must be inaccessible to vendor modules.
  This is the replacement for VNDK-Indirect, which was defined as an
  alias of VNDK previously.

* VNDK-SP-Private stands for the VNDK shared libraries that can be used
  by other VNDK-SP shared libraries but must be inaccessible to vendor
  modules.  This is the replacement for VNDK-SP-Indirect-Private.

This commit also renames:

* LL-NDK-Indirect          --> LL-NDK-Private
* VNDK-Indirect            --> VNDK-Private
* VNDK-SP-Indirect-Private --> VNDK-SP-Private

Test: ./tests/run.py
Change-Id: I499d39e393cf265d59ec529e69ea15b670384e99