openrisc: implement irqdomains

This moves OpenRISC to using the irqdomain infrastructure.  This doesn't
fundamentally change anything other than that it will be easier to have
multiple interrupt controllers in the future.

Signed-off-by: Jonas Bonn <jonas@southpole.se>

arch/openrisc/Kconfig

@@ -7,6 +7,7 @@ config OPENRISC
 	def_bool y
 	select OF
 	select OF_EARLY_FLATTREE
+	select IRQ_DOMAIN
 	select HAVE_MEMBLOCK
 	select ARCH_WANT_OPTIONAL_GPIOLIB
         select HAVE_ARCH_TRACEHOOK