ppc: Move mpc5xxx clocks to arch_global_data

Move ipb_clk and pci_clk into arch_global_data and tidy up.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/powerpc/cpu/mpc5xxx/i2c.c b/arch/powerpc/cpu/mpc5xxx/i2c.c
index b423d2f..8d5f47b 100644
--- a/arch/powerpc/cpu/mpc5xxx/i2c.c
+++ b/arch/powerpc/cpu/mpc5xxx/i2c.c
@@ -310,7 +310,7 @@
 			{126, 128}
 		};
 
-		ipb = gd->ipb_clk;
+		ipb = gd->arch.ipb_clk;
 		for (i = 7; i >= 0; i--) {
 			for (j = 7; j >= 0; j--) {
 				scl = 2 * (scltap[j].scl2tap +