arm: Move uart_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/ppc4xx/fdt.c b/arch/powerpc/cpu/ppc4xx/fdt.c
index 5ddb880..37f5817 100644
--- a/arch/powerpc/cpu/ppc4xx/fdt.c
+++ b/arch/powerpc/cpu/ppc4xx/fdt.c
@@ -141,7 +141,7 @@
 
 	/*
 	 * Fixup all UART clocks for CPU internal UARTs
-	 * (only these UARTs are definitely clocked by gd->uart_clk)
+	 * (only these UARTs are definitely clocked by gd->arch.uart_clk)
 	 *
 	 * These UARTs are direct childs of /plb/opb. This code
 	 * does not touch any UARTs that are connected to the ebc.
@@ -160,7 +160,7 @@
 		    (fdt_node_check_compatible(blob, off, "ns16550") == 0))
 			fdt_setprop(blob, off,
 				    "clock-frequency",
-				    (void*)&(gd->uart_clk), 4);
+				    (void *)&gd->arch.uart_clk, 4);
 	}
 
 	/*