arm-ccn: Enable building as module

arm-ccn driver uses irq_set_affinity, which is not exported and
hence cannot be built as a module, eventhough we have all the
bits ready. This patch makes use of the exported helper
irq_set_affinity_hint() instead. Also, the __free_irq expects
the affinity_hint to be NULL when we free the irq. So set the
affinity_hint to NULL at clean up.

Now that we can build it as a module, update the Kconfig to
reflect the change.

Cc: Will Deacon <will.deacon@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Acked-by: Pawel Moll <pawel.moll@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
diff --git a/drivers/bus/Kconfig b/drivers/bus/Kconfig
index f5ea153..c5a7de9b 100644
--- a/drivers/bus/Kconfig
+++ b/drivers/bus/Kconfig
@@ -48,7 +48,7 @@
 	  If unsure, say Y
 
 config ARM_CCN
-	bool "ARM CCN driver support"
+	tristate "ARM CCN driver support"
 	depends on ARM || ARM64
 	depends on PERF_EVENTS
 	help