mn10300: use RTC_DRV_CMOS instead of CONFIG_RTC

nn10300 has a dependency on mc146818_get_time/mc146818_set_time,
which we want to move from the mc146818rtc.h header into the
rtc subsystem, which in turn is not usable on mn10300.

This changes mn10300 to use the modern rtc-cmos driver instead
of the old RTC driver, and that in turn lets us completely
remove the read_persistent_clock/update_persistent_clock callbacks.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
diff --git a/arch/mn10300/Kconfig b/arch/mn10300/Kconfig
index 9627e81..38e3494 100644
--- a/arch/mn10300/Kconfig
+++ b/arch/mn10300/Kconfig
@@ -236,7 +236,9 @@
 config MN10300_RTC
 	bool "Using MN10300 RTC"
 	depends on MN10300_PROC_MN103E010 || MN10300_PROC_MN2WS0050
-	select GENERIC_CMOS_UPDATE
+	select RTC_CLASS
+	select RTC_DRV_CMOS
+	select RTC_SYSTOHC
 	default n
 	help
 	  This option enables support for the RTC, thus enabling time to be