CVE-2025-68333: sched_ext: Fix possible deadlock in the deferred_irq_workfn()

In the Linux kernel, the following vulnerability has been resolved:

schedext: Fix possible deadlock in the deferredirqworkfn()

For PREEMPTRT=y kernels, the deferredirqworkfn() is executed in the per-cpu irqwork/ task context and not disable-irq, if the rq returned by containerof() is current CPU's rq, the following scenarios may occur:

lock(&rq->lock); <Interrupt> lock(&rq->lock);

This commit use IRQWORKINITHARD() to replace initirqwork() to initialize rq->scx.deferredirqwork, make the deferredirqworkfn() is always invoked in hard-irq context.