ppc: Move mpc512x clocks to arch_global_data

Move ips_clk and csb_clk into arch_global_data and tidy up.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/powerpc/cpu/mpc512x/i2c.c b/arch/powerpc/cpu/mpc512x/i2c.c
index 0ea1280..59040f8 100644
--- a/arch/powerpc/cpu/mpc512x/i2c.c
+++ b/arch/powerpc/cpu/mpc512x/i2c.c
@@ -250,7 +250,7 @@
 			{126, 128}
 		};
 
-		ips = gd->ips_clk;
+		ips = gd->arch.ips_clk;
 		for (i = 7; i >= 0; i--) {
 			for (j = 7; j >= 0; j--) {
 				scl = 2 * (scltap[j].scl2tap +