x86/softirq: Move softirq pending next to current task

Another hot variable which is strict per CPU and benefits from
being in the same cache line.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220915111145.702133710@infradead.org