enum-ify stack/include/btm_api_types::BTM_SEC_

Towards readable code

Bug: 163134718
Tag: #refactor
Test: act.py -tc BleCocTest
Test: ble paired 2 phones
Test: classic paired Bose SoundLink
Change-Id: I6b7d23ffdd22b4d9e98f214f2fee650ea35d765d