Revert "ANDROID: sched: Move scratch_mask to a percpu variable"

This reverts commit 08ef1640.

This series is responsible for a functional regression with task
affinity failing to take into account offline CPUs. Although this has
been reported upstream, work to fix the problem is ongoing and we're
better off reverting these changes from android13-5.15.

Link: https://lore.kernel.org/lkml/20230131221719.3176-1-will@kernel.org/


Signed-off-by: Will Deacon <willdeacon@google.com>
Bug: 263926519
Bug: 264940090
Bug: 269965532
Change-Id: I521119817f3e6c107984197a8c0b170430f5b702