Tweak IRemotelyProvisionedComponent AIDL docs

 - Use P-256 in MacedPublicKey: The main place that MacedPublicKey is
   used requires a P-256 key, so use that as the example in the comment.
 - Fix leaf key type comment
 - Fix AES key size comment
 - Typo fix

Test: none, just comment change
Change-Id: I47a810f2a965facad6ddcd251341f233884e5f7c