powerpc/64s: move ret_from_fork etc above __end_soft_masked

Code which runs with interrupts enabled should be moved above
__end_soft_masked where possible, because maskable interrupts that hit
below that symbol will need to consult the soft mask table, which is an
extra cost.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210630074621.2109197-10-npiggin@gmail.com