arm64: kconfig: drop CONFIG_RTC_LIB dependency

The rtc-lib dependency is not required, and seems it was just
copy-pasted from ARM's Kconfig. If platform requires rtc-lib,
they should select it individually.
Reviewed-by: NArnd Bergmann <arnd@arndb.de>
Signed-off-by: NEzequiel Garcia <ezequiel@vanguardiasur.com.ar>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

arch/arm64/Kconfig

@@ -99,7 +99,6 @@ config ARM64
 	select PERF_USE_VMALLOC
 	select POWER_RESET
 	select POWER_SUPPLY
-	select RTC_LIB
 	select SPARSE_IRQ
 	select SYSCTL_EXCEPTION_TRACE
 	help