ARM: S5P: Fix export.h inclusion

Commit 32aaeffb ("Merge branch 'modsplit-Oct31 2011'...")
breaks build like following and this fixes it to add inclusion
<linux/export.h>.

arch/arm/plat-s5p/sysmmu.c:302: error: 'THIS_MODULE' undeclared here (not in a function)
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>

arch/arm/plat-s5p/sysmmu.c

@@ -11,6 +11,7 @@
 #include <linux/io.h>
 #include <linux/interrupt.h>
 #include <linux/platform_device.h>
+#include <linux/export.h>
 
 #include <asm/pgtable.h>