powerpc: Remove redundant selection of E500 and E500MC

PPC_85xx and PPC_BOOK3E_64 already select E500 so no need
to select it again by PPC_QEMU_E500 and CORENET_GENERIC
as they depend on PPC_85xx || PPC_BOOK3E_64.

PPC_BOOK3E_64 already selects E500MC so no need to
select it again by PPC_QEMU_E500 if PPC64, PPC_BOOK3E_64
is the only way into PPC_QEMU_E500 with PPC64.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/44f03fa1506892fabf626dceb2f47a049908b6af.1663606876.git.christophe.leroy@csgroup.eu