irq_domain: Centralize definition of irq_dispose_mapping()

Several architectures define their own empty irq_dispose_mapping().  Since
the irq_domain code is centralized now, there is little need to do so.  This
patch removes them and creates a new empty copy when !CONFIG_IRQ_DOMAIN is
selected.

The patch also means that IRQ_DOMAIN becomes selectable on all architectures.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Cc: Rob Herring <rob.herring@calxeda.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jonas Bonn <jonas@southpole.se>
Cc: sparclinux@vger.kernel.org
Cc: linux@lists.openrisc.net

arch/openrisc/include/asm/prom.h

@@ -24,6 +24,7 @@
 
 #include <linux/types.h>
 #include <asm/irq.h>
+#include <linux/irqdomain.h>
 #include <linux/atomic.h>
 #include <linux/of_irq.h>
 #include <linux/of_fdt.h>
@@ -63,15 +64,6 @@ extern const void *of_get_mac_address(struct device_node *np);
 struct pci_dev;
 extern int of_irq_map_pci(struct pci_dev *pdev, struct of_irq *out_irq);
 
-/* This routine is here to provide compatibility with how powerpc
- * handles IRQ mapping for OF device nodes.  We precompute and permanently
- * register them in the platform_device objects, whereas powerpc computes them
- * on request.
- */
-static inline void irq_dispose_mapping(unsigned int virq)
-{
-}
-
 #endif /* __ASSEMBLY__ */
 #endif /* __KERNEL__ */
 #endif /* _ASM_OPENRISC_PROM_H */