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/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
index 9f8b59d..13128a8 100644
--- a/drivers/rtc/Kconfig
+++ b/drivers/rtc/Kconfig
@@ -807,7 +807,7 @@
 
 config RTC_DRV_CMOS
 	tristate "PC-style 'CMOS'"
-	depends on X86 || ARM || M32R || PPC || MIPS || SPARC64
+	depends on X86 || ARM || M32R || PPC || MIPS || SPARC64 || MN10300
 	default y if X86
 	help
 	  Say "yes" here to get direct support for the real time clock