powerpc/32s: Regroup 603 based CPUs in cputable

In order to selectively build the kernel for 603 SW TLB handling,
regroup all 603 based CPUs together.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/45065263fdb9f5cc2a2d210ec2a762ac8bf5b2bc.1603348103.git.christophe.leroy@csgroup.eu