x86 setup: display VESA graphics modes in vga=ask menu

Display VESA graphics modes, with their mode IDs, in the vga=ask
menu.  Most VESA mode numbers are platform-dependent, so it helps to
have an easy way to display them.

Based in part on a patch by Petr Vandrovec <petr@vandrovec.name>.

Cc: Petr Vandrovec <petr@vandrovec.name>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/boot/video.h

@@ -83,7 +83,8 @@ void store_screen(void);
 
 struct mode_info {
 	u16 mode;		/* Mode number (vga= style) */
-	u8  x, y;		/* Width, height */
+	u16 x, y;		/* Width, height */
+	u16 depth;		/* Bits per pixel, 0 for text mode */
 };
 
 struct card_info {