irqchip/riscv-intc: Add missing free() callback in riscv_intc_domain_ops

irqchip/riscv-intc: Add missing free() callback in riscv_intc_domain_ops

The irq_domain_free_irqs() helper requires that the irq_domain_ops->free
callback is implemented. Otherwise, the kernel reports the warning message
"NULL pointer, cannot free irq" when irq_dispose_mapping() is invoked to
release the per-HART local interrupts.

Set irq_domain_ops->free to irq_domain_free_irqs_top() to cure that.

Fixes: 832f15f42646 ("RISC-V: Treat IPIs as normal Linux IRQs")
Signed-off-by: Nick Hu <nick.hu@sifive.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://patch.msgid.link/20251114-rv-intc-fix-v1-1-a3edd1c1a868@sifive.com