s390/time: Add clocksource id to TOD clock

To allow specifying the clock source in the upcoming PtP driver,
add a clocksource ID to the s390 TOD clock.

Acked-by: Heiko Carstens <hca@linux.ibm.com>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Link: https://patch.msgid.link/20241023065601.449586-2-svens@linux.ibm.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>