Add getKeyCharacteristics stub to km_compat

Add a stub implementation of getKeyCharacteristics which simply returns
UNIMPLEMENTED. A future change will hook this into the Keymaster
method getKeyCharacteristics.

(cherry picked from commit 48d9ff948f77461a4ead4ec99386d7c7cf2f9c7b)

Bug: 186685601
Test: Treehugger
Ignore-AOSP-First: Implementation exists in internal master only
Merged-In: I24496e6d67eeaeec610998c0139f36f216c621b0
Change-Id: I24496e6d67eeaeec610998c0139f36f216c621b0
2 files changed