Refactor: make makeGen local

No need for KeyUtil to know how to make a KeyGeneration, it's cleaner
if each module handles it separately. Also, create a CryptoOptions
structure to track metadata encryption options, and simplify legacy
cipher/option handling.

Test: Treehugger
Bug: 147814592
Change-Id: I740063882914097329ff72348d0c0855c26c7aab