ppc: Move brg_clk to arch_global_data

Move this field into arch_global_data and tidy up.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/powerpc/cpu/mpc8xx/fdt.c b/arch/powerpc/cpu/mpc8xx/fdt.c
index 7130983..7edd7e4 100644
--- a/arch/powerpc/cpu/mpc8xx/fdt.c
+++ b/arch/powerpc/cpu/mpc8xx/fdt.c
@@ -37,7 +37,7 @@
 	do_fixup_by_prop_u32(blob, "device_type", "cpu", 4,
 		"clock-frequency", bd->bi_intfreq, 1);
 	do_fixup_by_compat_u32(blob, "fsl,cpm-brg", "clock-frequency",
-		gd->brg_clk, 1);
+		gd->arch.brg_clk, 1);
 
 	/* Fixup ethernet MAC addresses */
 	fdt_fixup_ethernet(blob);
diff --git a/arch/powerpc/cpu/mpc8xx/speed.c b/arch/powerpc/cpu/mpc8xx/speed.c
index 6e13e5d..091b49f 100644
--- a/arch/powerpc/cpu/mpc8xx/speed.c
+++ b/arch/powerpc/cpu/mpc8xx/speed.c
@@ -192,7 +192,7 @@
 			divider = 64;
 			break;
 	}
-	gd->brg_clk = gd->cpu_clk/divider;
+	gd->arch.brg_clk = gd->cpu_clk/divider;
 }
 
 #if !defined(CONFIG_8xx_CPUCLK_DEFAULT)