Force Software Rendering for KeyguardClockFrame

Using hardware rendering disables the ability to intercept alpha
and handle it seperately. Enforcing a software layer for the view
in question prevents this from happening.

Bug: 288233136
Test: Manually tested the new setting
Change-Id: I8e1ea0769bdba27e880eea642176fdd2c25bfca4
Merged-In: I8e1ea0769bdba27e880eea642176fdd2c25bfca4