[POWERPC] Implement {read,update}_persistent_clock

With these functions implemented we cooperate better with the generic
timekeeping code.  This obsoletes the need for the timer sysdev as a bonus.

Signed-off-by: Tony Breeds <tony@bakeyournoodle.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 45e86c7..6468cd9 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -26,6 +26,9 @@
 	bool
 	default y
 
+config GENERIC_CMOS_UPDATE
+	def_bool y
+
 config GENERIC_HARDIRQS
 	bool
 	default y