enum-ify stack/btm/security_device_record::BTM_SEC_STATE_

Towards readable code

Bug: 163134718
Tag: #refactor
Test: act.py -tc BleCocTest
Test: ble paired 2 phones
Test: classic paired Bose SoundLink
Change-Id: I2b44dfca2d36c815d65c786ca7371cc24788bcca