irq_domain/powerpc: Use common irq_domain structure instead of irq_host

This patch drops the powerpc-specific irq_host structures and uses the common
irq_domain strucutres defined in linux/irqdomain.h.  It also fixes all
the users to use the new structure names.

Renaming irq_host to irq_domain has been discussed for a long time, and this
patch is a step in the process of generalizing the powerpc virq code to be
usable by all architecture.

An astute reader will notice that this patch actually removes the irq_host
structure instead of renaming it.  This is because the irq_domain structure
already exists in include/linux/irqdomain.h and has the needed data members.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Milton Miller <miltonm@bga.com>
Tested-by: Olof Johansson <olof@lixom.net>

arch/powerpc/include/asm/i8259.h

@@ -6,7 +6,7 @@
 
 extern void i8259_init(struct device_node *node, unsigned long intack_addr);
 extern unsigned int i8259_irq(void);
-extern struct irq_host *i8259_get_host(void);
+extern struct irq_domain *i8259_get_host(void);
 
 #endif /* __KERNEL__ */
 #endif /* _ASM_POWERPC_I8259_H */