hw/ppc/Makefile: Add a way to disable the PPC4xx boards

We've got the config switch CONFIG_PPC4XX, so we should use it
in the Makefile accordingly and only include the PPC4xx boards
if this switch has been enabled. (Note: Unfortunately, the files
ppc4xx_devs.c and ppc405_uc.c still have to be included in the
build anyway to fulfil some complicated linker dependencies ...
so these are subject to a more thourough clean-up later)
Signed-off-by: NThomas Huth <thuth@redhat.com>
Signed-off-by: NDavid Gibson <david@gibson.dropbear.id.au>

hw/ppc/Makefile.objs

@@ -12,8 +12,8 @@ obj-y += spapr_pci_vfio.o
 endif
 obj-$(CONFIG_PSERIES) += spapr_rtas_ddw.o
 # PowerPC 4xx boards
-obj-y += ppc405_boards.o ppc4xx_devs.o ppc405_uc.o ppc440_bamboo.o
-obj-y += ppc4xx_pci.o
+obj-y += ppc4xx_devs.o ppc405_uc.o
+obj-$(CONFIG_PPC4XX) += ppc4xx_pci.o ppc405_boards.o ppc440_bamboo.o
 # PReP
 obj-$(CONFIG_PREP) += prep.o
 obj-$(CONFIG_PREP) += prep_systemio.o