powerpc/cputable: Split cpu_specs[] for mpc85xx and e500mc

e500v1/v2 and e500mc are said to be mutually exclusive in Kconfig.

Split e500 cpu_specs[] and then restrict the non e500mc to PPC32
which is then 85xx.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
[mpe: Tweak formatting]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/553b901ea91e393df231103da4b018e9b251b0e9.1663606876.git.christophe.leroy@csgroup.eu