powerpc: fix building hvc_opal.c

Fix building following build error:

  drivers/tty/hvc/hvc_opal.c:244:12: error: 'THIS_MODULE' undeclared here (not in a function)
Signed-off-by: NMichael Neuling <mikey@neuling.org>
[ New file from powerpc tree not following the new rules from the
  module.h split, both of which were merged today.  - Linus ]
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

drivers/tty/hvc/hvc_opal.c

@@ -28,6 +28,7 @@
 #include <linux/console.h>
 #include <linux/of.h>
 #include <linux/of_platform.h>
+#include <linux/export.h>
 
 #include <asm/hvconsole.h>
 #include <asm/prom.h>