This patch adds the SecurityLevelEnum to KeyProperties. This enum can be
used by the public API surface to express levels of enforcements of key
properties. And to select a designated residence for a newly generated
or imported key.
The values UNKNOWN and UNKNOWN_SECURE are used to convey to older target
APIs API levels that have not been defined when they where published.
Test: None
Change-Id: I88681f21b8a8ea9a383d32ba99f3ab7d7c8909c3
d2c944bc4d