[pre_freeze] Clean up checks for enabling PreFreeze

We check for both platform support (Android U+) and for whether the
correct feature is enabled. Previously, we checked for each of these
conditions separately. Now, we check for both in one helper function.

Bug: 1513796
Change-Id: If401f90629a4823fc7c5eec4e586d2cc5fef7914
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5374781


Commit-Queue: Thiabaud Engelbrecht <thiabaud@google.com>
Reviewed-by: Benoit Lize <lizeb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1278951}