init: Log shutdown time using klog before kernel reboot

This CL makes logShutdownTime() using klog to prevent log data loss
during kernel reboot/shutdown to ensure the log message is perserved
after reboot.

This Cl also makes `LogShutdownTime` function moved to just before the
system reboots or shuts down, making the shutdown time measurement more
accurate.

Additionally, logging is also performed if the data filesystem type is
empty or shutdown timeout. This ensures consistent logging of shutdown
time regardless of the shutdown path.

Bug: 409182226
Test: adb reboot & verify shutdown time in pstore log (userdebug build)
Change-Id: Iadebddfda4ddbaf903a72b9dc5f1add4040286d3