feat: enable PCF8523 RTC support for arm64

Enable the in-tree PCF8523 RTC driver on arm64 so devices described by
the device tree can be registered as Linux RTC devices.

Signed-off-by: ctr49 <ctr49@users.noreply.github.com>
Signed-off-by: Andrey Smirnov <andrey.smirnov@siderolabs.com>
(cherry picked from commit b253464)

Author: ctr49

kernel/build/config-arm64

@@ -7338,7 +7338,7 @@ CONFIG_RTC_DRV_RK808=y
 # CONFIG_RTC_DRV_ISL12022 is not set
 # CONFIG_RTC_DRV_ISL12026 is not set
 # CONFIG_RTC_DRV_X1205 is not set
-# CONFIG_RTC_DRV_PCF8523 is not set
+CONFIG_RTC_DRV_PCF8523=y
 # CONFIG_RTC_DRV_PCF85363 is not set
 # CONFIG_RTC_DRV_PCF8563 is not set
 # CONFIG_RTC_DRV_PCF8583 is not set