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/rtc-cmos.c b/drivers/rtc/rtc-cmos.c
index cf8eb98..f9fdb6f 100644
--- a/drivers/rtc/rtc-cmos.c
+++ b/drivers/rtc/rtc-cmos.c
@@ -630,7 +630,7 @@
 	address_space = 64;
 #elif defined(__i386__) || defined(__x86_64__) || defined(__arm__) \
 			|| defined(__sparc__) || defined(__mips__) \
-			|| defined(__powerpc__)
+			|| defined(__powerpc__) || defined(CONFIG_MN10300)
 	address_space = 128;
 #else
 #warning Assuming 128 bytes of RTC+NVRAM address space, not 64 bytes.