lib: sbi_irqchip: Set the IRQ handler when registering a chip

In addition to saving some code size, this moves the decision about
setting the top-level external interrupt handler to the irqchip core,
not the specific driver, which would be needed to support chained
interrupt handlers.

Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
Reviewed-by: Anup Patel <anup@brainfault.org>

include/sbi/sbi_irqchip.h

@@ -22,17 +22,10 @@ struct sbi_irqchip_device {
 
 	/** Initialize per-hart state for the current hart */
 	int (*warm_init)(struct sbi_irqchip_device *dev);
-};
 
-/**
- * Set external interrupt handling function
- *
- * This function is called by OpenSBI platform code to set a handler for
- * external interrupts
- *
- * @param fn function pointer for handling external irqs
- */
-void sbi_irqchip_set_irqfn(int (*fn)(void));
+	/** Handle an IRQ from this irqchip */
+	int (*irq_handle)(void);
+};
 
 /**
  * Process external interrupts