global_data: Move pci_clk to m68k and powerpc

Only m68k and powerpc use this field, so move it to the arch-specific
info, to reduce the size for other archs.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/clk/mpc83xx_clk.c b/drivers/clk/mpc83xx_clk.c
index a29ad0d..a43fff2 100644
--- a/drivers/clk/mpc83xx_clk.c
+++ b/drivers/clk/mpc83xx_clk.c
@@ -358,7 +358,7 @@
 	gd->mem_clk = priv->speed[MPC83XX_CLK_MEM];
 
 	if (mpc83xx_has_pci(type))
-		gd->pci_clk = priv->speed[MPC83XX_CLK_PCI];
+		gd->arch.pci_clk = priv->speed[MPC83XX_CLK_PCI];
 
 	gd->cpu_clk = priv->speed[MPC83XX_CLK_CORE];
 	gd->bus_clk = priv->speed[MPC83XX_CLK_CSB];