[console] Allow console input and output to be disabled independently

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/arch/i386/core/video_subr.c

@@ -104,7 +104,7 @@ static void vga_putc(int byte)
 
 struct console_driver vga_console __console_driver = {
 	.putchar = vga_putc,
-	.disabled = 1,
+	.disabled = CONSOLE_DISABLED,
 	.usage = CONSOLE_DIRECT_VGA,
 };