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/drivers/qe/qe.c b/drivers/qe/qe.c
index 345587b..72c585c 100644
--- a/drivers/qe/qe.c
+++ b/drivers/qe/qe.c
@@ -220,7 +220,7 @@
    from CLKn pin, we have te change the function.
  */
 
-#define BRG_CLK		(gd->brg_clk)
+#define BRG_CLK		(gd->arch.brg_clk)
 
 int qe_set_brg(uint brg, uint rate)
 {