Enable CONFIG_MEM_SOFT_DIRTY to get some test coverage. Distros enable
it, and it has been broken previously. See commit 66b2ca08
("powerpc/64s/radix: Fix soft dirty tracking").
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20231024112726.1819795-1-mpe@ellerman.id.au