A later change stops the kernel using r2 and loads it with a poison
value.  Provide a PACATOC loading abstraction which can hide this
detail.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220926034057.2360083-5-npiggin@gmail.com