Start adding documentation for IFingerprint

Minor changes to interface:
1) IResetLockoutCallback renamed to ILockoutCallback
2) Removes unnecessary parameter from onChallengeGenerated
3) Adds "challenge" param to revokeChallenge to support multiple
   in-flight challenges

Bug: 168842956
Bug: 168843220

Test: make -j56 android.hardware.biometrics.fingerprint-update-api
Test: make -j
Test: make -j56 VtsHalBiometricsFingerprintTargetTest

Change-Id: If1f63a6d0c135d7b59690a31728b4d3fc8c2d2c4