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/arch/m68k/cpu/mcf5445x/cpu.c b/arch/m68k/cpu/mcf5445x/cpu.c
index b811ac3..3fbd6a5 100644
--- a/arch/m68k/cpu/mcf5445x/cpu.c
+++ b/arch/m68k/cpu/mcf5445x/cpu.c
@@ -92,7 +92,7 @@
 		       strmhz(buf3, gd->arch.flb_clk));
 #ifdef CONFIG_PCI
 		printf("       PCI CLK %s MHz INP CLK %s MHz VCO CLK %s MHz\n",
-		       strmhz(buf1, gd->pci_clk),
+		       strmhz(buf1, gd->arch.pci_clk),
 		       strmhz(buf2, gd->arch.inp_clk),
 		       strmhz(buf3, gd->arch.vco_clk));
 #else