hw/ppc/Kconfig: Let the Sam460ex board use the PowerPC 405 devices

hw/ppc/Kconfig: Let the Sam460ex board use the PowerPC 405 devices

When configured with --without-default-devices, the build fails:

    LINK    ppc-softmmu/qemu-system-ppc
  /usr/bin/ld: hw/ppc/sam460ex.o: in function `sam460ex_init':
  hw/ppc/sam460ex.c:313: undefined reference to `ppc4xx_plb_init'
  /usr/bin/ld: hw/ppc/sam460ex.c:353: undefined reference to `ppc405_ebc_init'
  collect2: error: ld returned 1 exit status
  make[1]: *** [Makefile:206: qemu-system-ppc] Error 1

Fix by selecting the PPC405 config.

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20191231183216.6781-8-philmd@redhat.com>
Reviewed-by: BALATON Zoltan <balaton@eik.bme.hu>
Acked-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>