Fix caching interface according to vendor feedback.

- 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.

Bug: 123780248
Test: VtsHalNeuralnetworksV1_xTargetTest with 1.2 sample driver
Test: VtsHalNeuralnetworksV1_xTargetTest with a test driver that can
      read and write cache entries
Change-Id: I921b7b8ccc3c66af19f6589f7213c6870d6f07bf