powerpc/pseries: lparcfg don't include slb_size line in radix mode

This avoids a change in behaviour in the later patch making hash
support configurable. This is possibly a user interface change, so
the alternative would be a hard-coded slb_size=0 here.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211201144153.2456614-7-npiggin@gmail.com