irq_domain/c6x: Convert c6x to use generic irq_domain support.

The C6X IRQ support was copied almost verbatim from the PowerPC virtual IRQ
code. The PowerPC code was used as the basis for generic irq_domain support,
so this patch mostly copies what what done to arch/powerpc by Grant Likely
in his irq_domain patch series.

Signed-off-by: Mark Salter <msalter@redhat.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Cc: Aurelien Jacquiot <a-jacquiot@ti.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
diff --git a/arch/c6x/Kconfig b/arch/c6x/Kconfig
index 26e67f0..3c64b28 100644
--- a/arch/c6x/Kconfig
+++ b/arch/c6x/Kconfig
@@ -12,6 +12,7 @@
 	select HAVE_GENERIC_HARDIRQS
 	select HAVE_MEMBLOCK
 	select HAVE_SPARSE_IRQ
+	select IRQ_DOMAIN
 	select OF
 	select OF_EARLY_FLATTREE