s390: Select POSIX_CPU_TIMERS_TASK_WORK

After support for VIRT_XFER_TO_GUEST_WORK is available for s390 it is
possible to also select HAVE_POSIX_CPU_TIMERS_TASK_WORK. See [1] for the
reasons why it makes sense, also for architectures which do not support
PREEMPT_RT.

[1] https://lore.kernel.org/all/[e-mail]

Signed-off-by: Heiko Carstens <[e-mail]>

arch/s390/Kconfig

···
 	select HAVE_PERF_EVENTS
 	select HAVE_PERF_REGS
 	select HAVE_PERF_USER_STACK_DUMP
+	select HAVE_POSIX_CPU_TIMERS_TASK_WORK
 	select HAVE_PREEMPT_DYNAMIC_KEY
 	select HAVE_REGS_AND_STACK_ACCESS_API
 	select HAVE_RELIABLE_STACKTRACE