mips: add export.h to files using EXPORT_SYMBOL/THIS_MODULE

Or else we get lots of variations on this:

arch/mips/pci/pci.c:330: warning: type defaults to 'int' in declaration of 'EXPORT_SYMBOL'

scattered throughout the build.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
diff --git a/arch/mips/cavium-octeon/dma-octeon.c b/arch/mips/cavium-octeon/dma-octeon.c
index 1abb66c..ea4feba 100644
--- a/arch/mips/cavium-octeon/dma-octeon.c
+++ b/arch/mips/cavium-octeon/dma-octeon.c
@@ -13,6 +13,7 @@
 #include <linux/dma-mapping.h>
 #include <linux/scatterlist.h>
 #include <linux/bootmem.h>
+#include <linux/export.h>
 #include <linux/swiotlb.h>
 #include <linux/types.h>
 #include <linux/init.h>