Fix caching interface according to vendor feedback.

There are three major changes

- Instead of isCachingSupport returning a single boolean, switch to
  getNumberOfCacheFilesNeeded returning the number of cache files. This
  is to support use cases when driver needs more than one cache file for
  each type, or when driver does not need data cache.

- Instead of a separate saveToCache, pass cache info along with
  prepareModel_1_2 to save into cache as well as perform compilation.
  This is to avoid a potential additional copy of cache files.

- Grant RDWR permission for prepareModelFromCache and prepareModel_1_2.
  This is for the driver to be able to read/update later, e.g.
  multi-stage compilation that does a fast compilation first and refines
  later.

Bug: 123780248
Test: NeuralNetworksTest_static
Change-Id: Id370919b742a60bf1f3277c3bc6bda1e8475f1da