powerpc/rfi-flush: Call setup_rfi_flush() after LPM migration

commit 921bc6cf807ceb2ab8005319cf39f33494d6b100 upstream.

We might have migrated to a machine that uses a different flush type,
or doesn't need flushing at all.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Mauricio Faria de Oliveira <mauricfo@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>