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/rb532/setup.c b/arch/mips/rb532/setup.c
index 50f530f..d0c64e7 100644
--- a/arch/mips/rb532/setup.c
+++ b/arch/mips/rb532/setup.c
@@ -3,6 +3,7 @@
  */
 
 #include <linux/init.h>
+#include <linux/export.h>
 
 #include <asm/bootinfo.h>
 #include <asm/reboot.h>