sched: Fix build for modules using set_tsk_need_resched()

Commit adcc3bfa8806 ("sched: Adapt sched tracepoints for RV task model")
added a tracepoint to the need_resched action that can be triggered also
by set_tsk_need_resched.
This function was previously accessible from out-of-tree modules but
it's no longer available because the __trace_set_need_resched() symbol
is not exported (together with the tracepoint itself, which was exported
in a separate patch) and building such modules fails.

Export __trace_set_need_resched to modules to fix those build issues.

Fixes: adcc3bfa8806 ("sched: Adapt sched tracepoints for RV task model")
Signed-off-by: Gabriele Monaco <gmonaco@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Phil Auld <pauld@redhat.com>
Link: https://patch.msgid.link/20260112140413.362202-1-gmonaco@redhat.com