nios2: add screen_info

Fix build error when enable VGA console.

drivers/video/console/vgacon.c:586: undefined reference to `screen_info'

Signed-off-by: Ley Foon Tan <ley.foon.tan@intel.com>
diff --git a/arch/nios2/kernel/setup.c b/arch/nios2/kernel/setup.c
index a4ff86d..a3fa80d 100644
--- a/arch/nios2/kernel/setup.c
+++ b/arch/nios2/kernel/setup.c
@@ -18,6 +18,7 @@
 #include <linux/bootmem.h>
 #include <linux/initrd.h>
 #include <linux/of_fdt.h>
+#include <linux/screen_info.h>
 
 #include <asm/mmu_context.h>
 #include <asm/sections.h>
@@ -36,6 +37,10 @@
 					0, 0, 0, 0, 0, 0,
 					0};
 
+#ifdef CONFIG_VT
+struct screen_info screen_info;
+#endif
+
 /* Copy a short hook instruction sequence to the exception address */
 static inline void copy_exception_handler(unsigned int addr)
 {