MIPS: Loongson64: Mark RS780 HPET as broken

This driver is using some dangerous hack to set MMIO address for HPET,
which might break systems with other kinds of PCH.

Also, as Loongson-3 cpufreq driver never appeared in mainline,
this driver rarely got used.

So we temporarily mark it as broken until we find a better solution.
Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/loongson64/Kconfig

@@ -4,14 +4,12 @@ if MACH_LOONGSON64
 config RS780_HPET
 	bool "RS780/SBX00 HPET Timer"
 	depends on MACH_LOONGSON64
+	depends on BROKEN
 	select MIPS_EXTERNAL_TIMER
 	help
 	  This option enables the hpet timer of AMD RS780/SBX00.
 
-	  If you want to enable the Loongson3 CPUFreq Driver, Please enable
-	  this option at first, otherwise, You will get wrong system time.
-
-	  If unsure, say Yes.
-
+	  Note: This driver is doing some dangerous hack. Please only enable
+	  it on RS780E systems.
 
 endif # MACH_LOONGSON64