powerpc/irq: drop arch_early_irq_init()

arch_early_irq_init() does nothing different than the weak
arch_early_irq_init() in kernel/softirq.c

Fixes: 089fb442 ("powerpc: Use ARCH_IRQ_INIT_FLAGS")
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kernel/irq.c

@@ -827,11 +827,6 @@ int irq_choose_cpu(const struct cpumask *mask)
 }
 #endif
 
-int arch_early_irq_init(void)
-{
-	return 0;
-}
-
 #ifdef CONFIG_PPC64
 static int __init setup_noirqdistrib(char *str)
 {