sh: cpufreq: Fix driver dependencies and flag as broken.

This is only supported on SH-4, so don't expose it for the other
CPUs. Additionally, it's suffered some bitrot, so add a BROKEN
dependency as well until we fix it up.
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

arch/sh/Kconfig

@@ -474,7 +474,7 @@ source "drivers/cpufreq/Kconfig"
 
 config SH_CPU_FREQ
 	tristate "SuperH CPU Frequency driver"
-	depends on CPU_FREQ
+	depends on CPU_FREQ && CPU_SH4 && BROKEN
 	select CPU_FREQ_TABLE
 	help
 	  This adds the cpufreq driver for SuperH. At present, only