Hide backdrop when waking up from fp

When the display is off or in low power mode, and the user
wakes it up using fingerprint, we should go directly to
an unlocked state hiding whatever was visible on the backdrop.

You might be able to briefly see the backdrop otherwise.

Test: wake up from AOD with/without lockscreen image
Test: wake up from pulse with/without lockscreen image
Test: unlock with fp from lock screen
Change-Id: Ia27c80b32863c57461fb6aa74f6c31bf0803b6fb
Fixes: 80531298