irqchip/sifive-plic: Respect mask state when setting affinity

plic_set_affinity() always calls plic_irq_enable(), which clears up the
priority setting even the interrupt is only masked. This unmasks the
interrupt unexpectly.

Replace the plic_irq_enable/disable() with plic_irq_toggle() to avoid
changing the priority setting.

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Inochi Amaoto <inochiama@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Nam Cao <namcao@linutronix.de> # VisionFive 2
Tested-by: Chen Wang <unicorn_wang@outlook.com> # Pioneerbox
Reviewed-by: Nam Cao <namcao@linutronix.de>
Reviewed-by: Chen Wang <unicorn_wang@outlook.com>
Link: https://lore.kernel.org/all/20250811002633.55275-1-inochiama@gmail.com
Link: https://lore.kernel.org/lkml/20250722224513.22125-1-inochiama@gmail.com/