kernel: Enable CMOS RTC support on 5.4

Enable kernel symbol CONFIG_RTC_DRV_CMOS which was enabled in 4.14 &
4.19

Fixes FS#2905 and now my APU2 picks up time from RTC

Signed-off-by: Kevin Darbyshire-Bryant <ldir@darbyshire-bryant.me.uk>

target/linux/generic/config-5.4

@@ -4331,7 +4331,7 @@ CONFIG_RFKILL=y
 # CONFIG_RTC_DRV_BQ32K is not set
 # CONFIG_RTC_DRV_BQ4802 is not set
 # CONFIG_RTC_DRV_CADENCE is not set
-# CONFIG_RTC_DRV_CMOS is not set
+CONFIG_RTC_DRV_CMOS=y
 # CONFIG_RTC_DRV_DS1286 is not set
 # CONFIG_RTC_DRV_DS1302 is not set
 # CONFIG_RTC_DRV_DS1305 is not set