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/serial.c b/arch/powerpc/cpu/mpc512x/serial.c
index 58587fd..3afbe81 100644
--- a/arch/powerpc/cpu/mpc512x/serial.c
+++ b/arch/powerpc/cpu/mpc512x/serial.c
@@ -140,7 +140,7 @@
 	}
 
 	/* calculate divisor for setting PSC CTUR and CTLR registers */
-	baseclk = (gd->ips_clk + 8) / 16;
+	baseclk = (gd->arch.ips_clk + 8) / 16;
 	div = (baseclk + (baudrate / 2)) / baudrate;
 
 	out_8(&psc->ctur, (div >> 8) & 0xff);