EMB-237: build M41T80 RTC driver into kernel

Set CONFIG_RTC_DRV_M41T80=y so the external RTC (rtc1) is available
during early boot.

When this driver is built as a module, rtc1 is registered later and the
system clock is corrected mid-boot, causing a visible time jump.
Building it in allows hctosys to use rtc1 earlier and avoids that jump.

Author: bajosoto

configs/sx8m_defconfig

@@ -801,7 +801,7 @@ CONFIG_RTC_DRV_DS1307=m
 CONFIG_RTC_DRV_HYM8563=m
 CONFIG_RTC_DRV_MAX77686=y
 CONFIG_RTC_DRV_PCF85363=m
-CONFIG_RTC_DRV_M41T80=m
+CONFIG_RTC_DRV_M41T80=y
 CONFIG_RTC_DRV_RX8581=m
 CONFIG_RTC_DRV_RV3028=m
 CONFIG_RTC_DRV_RV8803=m