hrtimer: Use __raise_softirq_irqoff() to raise the softirq

Raising the hrtimer soft interrupt is always done from hard interrupt
context, so it can be reduced to just setting the HRTIMER soft interrupt
flag. The soft interrupt will be invoked on return from interrupt.

Use therefore __raise_softirq_irqoff() to raise the HRTIMER soft interrupt,
which is a trivial optimization.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/all/20241106150419.2593080-2-bigeasy@linutronix.de