[Flexiglass] Fix unlock icon shown on AOD when no lock setup on device

Issue - DeviceEntryIcon's alpha was 1f when KeyguardState was UNDEFINED
and Flexiglass was ENABLED

Fix - For KeyguardState UNDEFINED, if Flexiglass is ENABLED set alpha as
1f or 0f based on Scenes

Bug: 436820657
Test: Manually checked DeviceEntryIcon's alpha across various scenes
with AOD ON and OFF, it seems to be working as expected
Flag: EXEMPT bugfix

Change-Id: Ie27e8cea90e81f87c67dc55c5c55996eea8bf326