powerpc: add export.h to files making use of EXPORT_SYMBOL

With module.h being implicitly everywhere via device.h, the absence
of explicitly including something for EXPORT_SYMBOL went unnoticed.
Since we are heading to fix things up and clean module.h from the
device.h file, we need to explicitly include these files now.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
diff --git a/arch/powerpc/platforms/cell/axon_msi.c b/arch/powerpc/platforms/cell/axon_msi.c
index ac06903..40a6e34 100644
--- a/arch/powerpc/platforms/cell/axon_msi.c
+++ b/arch/powerpc/platforms/cell/axon_msi.c
@@ -13,6 +13,7 @@
 #include <linux/kernel.h>
 #include <linux/pci.h>
 #include <linux/msi.h>
+#include <linux/export.h>
 #include <linux/of_platform.h>
 #include <linux/debugfs.h>
 #include <linux/slab.h>