camera: Allow devices to load custom CameraParameter code

* Some devices need additional code to load their cameras. Add a hook
  for extra classes and symbols to be included.

Originally implemented in Android.mk at 38b27bf2e5079441358288402b38865ba7c1d9d6
Credit to Ethan Chen for original Android.mk implementation
Originally implemented via lineage product variable at 7398f91e
Credit to Rashed Abdel-Tawab for original product variable implementation

Change-Id: Iec667af2f0bfdb41f14df342cb128908244d7af0