powerpc: Introduce ppc_pci_flags accessors

Currently there are a number of platforms that open code access to
the ppc_pci_flags global variable.  However, that variable is not
present if CONFIG_PCI is not set, which can lead to a build break.

This introduces a number of accessor functions that are defined
to be empty in the case of CONFIG_PCI being disabled.  The
various platform files in the kernel are updated to use these.

Signed-off-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
diff --git a/arch/powerpc/platforms/chrp/pci.c b/arch/powerpc/platforms/chrp/pci.c
index 5a72ee5..f6b0c51 100644
--- a/arch/powerpc/platforms/chrp/pci.c
+++ b/arch/powerpc/platforms/chrp/pci.c
@@ -199,7 +199,7 @@
 		printk ("RTAS supporting Pegasos OF not found, please upgrade"
 			" your firmware\n");
 	}
-	ppc_pci_flags |= PPC_PCI_REASSIGN_ALL_BUS;
+	ppc_pci_add_flags(PPC_PCI_REASSIGN_ALL_BUS);
 	/* keep the reference to the root node */
 }