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>

arch/powerpc/mm/pgtable_64.c

@@ -26,6 +26,7 @@
 #include <linux/kernel.h>
 #include <linux/errno.h>
 #include <linux/string.h>
+#include <linux/export.h>
 #include <linux/types.h>
 #include <linux/mman.h>
 #include <linux/mm.h>