s390/time: Add PtP driver

s390/time: Add PtP driver

Add a small PtP driver which allows user space to get
the values of the physical and tod clock. This allows
programs like chrony to use STP as clock source and
steer the kernel clock. The physical clock can be used
as a debugging aid to get the clock without any additional
offsets like STP steering or LPAR offset.

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/20241023065601.449586-3-svens@linux.ibm.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>