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
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:89a0ae602061df09ede1e5138bf2e9a7c434260a)
Merged-In: I8e1ea0769bdba27e880eea642176fdd2c25bfca4
Change-Id: I8e1ea0769bdba27e880eea642176fdd2c25bfca4