console: fix up ARM screen_info reference

Separating the VGA console screen_info from the EFI one unfortunately
caused a build failure for footbridge that I had never caught
with randconfig builds:

arch/arm/kernel/setup.c:932:27: error: static declaration of 'vgacon_screen_info' follows non-static declaration
  932 | static struct screen_info vgacon_screen_info = {
      |                           ^~~~~~~~~~~~~~~~~~
In file included from arch/arm/kernel/setup.c:44:
arch/arm/include/asm/setup.h:40:27: note: previous declaration of 'vgacon_screen_info' with type 'struct screen_info'
   40 | extern struct screen_info vgacon_screen_info;
      |                           ^~~~~~~~~~~~~~~~~~
arm-linux-gnueabi-ld: drivers/video/console/dummycon.o: in function `dummycon_init':
dummycon.c:(.text+0xe4): undefined reference to `screen_info'

Make sure the variable is global to avoid the conflict with the extern
declaration, and make it work in dummycon.c
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20231017093947.3627976-2-arnd@kernel.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/arm/include/asm/vga.h

@@ -5,6 +5,7 @@
 #include <linux/io.h>
 
 extern unsigned long vga_base;
+extern struct screen_info vgacon_screen_info;
 
 #define VGA_MAP_MEM(x,s)	(vga_base + (x))
 

arch/arm/kernel/setup.c

@@ -929,7 +929,7 @@ static void __init request_standard_resources(const struct machine_desc *mdesc)
 }
 
 #if defined(CONFIG_VGA_CONSOLE)
-static struct screen_info vgacon_screen_info = {
+struct screen_info vgacon_screen_info = {
  .orig_video_lines	= 30,
  .orig_video_cols	= 80,
  .orig_video_mode	= 0,

drivers/video/console/dummycon.c

@@ -19,8 +19,9 @@
  */
 
 #if defined(CONFIG_ARCH_FOOTBRIDGE) && defined(CONFIG_VGA_CONSOLE)
-#define DUMMY_COLUMNS	screen_info.orig_video_cols
-#define DUMMY_ROWS	screen_info.orig_video_lines
+#include <asm/vga.h>
+#define DUMMY_COLUMNS	vgacon_screen_info.orig_video_cols
+#define DUMMY_ROWS	vgacon_screen_info.orig_video_lines
 #else
 /* set by Kconfig. Use 80x25 for 640x480 and 160x64 for 1280x1024 */
 #define DUMMY_COLUMNS	CONFIG_DUMMY_CONSOLE_COLUMNS