[ARM] footbridge: set dc21285 clock rate from command line

Allow the footbridge clock rate to be specified on the kernel command
line.  This allows us to work-around broken Personal Server firmware.
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

arch/arm/mach-footbridge/common.c

@@ -34,6 +34,13 @@ unsigned int mem_fclk_21285 = 50000000;
 
 EXPORT_SYMBOL(mem_fclk_21285);
 
+static void __init early_fclk(char **arg)
+{
+	mem_fclk_21285 = simple_strtoul(*arg, arg, 0);
+}
+
+__early_param("mem_fclk_21285=", early_fclk);
+
 static int __init parse_tag_memclk(const struct tag *tag)
 {
 	mem_fclk_21285 = tag->u.memclk.fmemclk;