padata: fix possible padata_works_lock deadlock

syzbot reports,

  WARNING: inconsistent lock state
  5.9.0-rc2-syzkaller #0 Not tainted
  --------------------------------
  inconsistent {IN-SOFTIRQ-W} -> {SOFTIRQ-ON-W} usage.
  syz-executor.0/26715 takes:
  (padata_works_lock){+.?.}-{2:2}, at: padata_do_parallel kernel/padata.c:220
  {IN-SOFTIRQ-W} state was registered at:
    spin_lock include/linux/spinlock.h:354 [inline]
    padata_do_parallel kernel/padata.c:220
    ...
    __do_softirq kernel/softirq.c:298
    ...
    sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1091
    asm_sysvec_apic_timer_interrupt arch/x86/include/asm/idtentry.h:581

   Possible unsafe locking scenario:

         CPU0
         ----
    lock(padata_works_lock);
    <Interrupt>
      lock(padata_works_lock);

padata_do_parallel() takes padata_works_lock with softirqs enabled, so a
deadlock is possible if, on the same CPU, the lock is acquired in
process context and then softirq handling done in an interrupt leads to
th...