Update keyguard root view alpha if udfps refactor flag is enabled

Flag: ACONFIG com.android.systemui.device_entry_udfps_refactor TEAMFOOD
Test: manually disable keyguard_bottom_area flag and enable
device_entry_udfps_refactor flag. Swipe up on the device
with just an unlock icon and see device entry icon fades.
Fixes: 329365118

Change-Id: If832d140a8b85237a33806ec5b038d04d397b2ca