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/40x/ppc40x_simple.c b/arch/powerpc/platforms/40x/ppc40x_simple.c
index 4498a86..f40ac9b 100644
--- a/arch/powerpc/platforms/40x/ppc40x_simple.c
+++ b/arch/powerpc/platforms/40x/ppc40x_simple.c
@@ -61,7 +61,7 @@
 
 	for (i = 0; i < ARRAY_SIZE(board); i++) {
 		if (of_flat_dt_is_compatible(root, board[i])) {
-			ppc_pci_flags = PPC_PCI_REASSIGN_ALL_RSRC;
+			ppc_pci_set_flags(PPC_PCI_REASSIGN_ALL_RSRC);
 			return 1;
 		}
 	}