Create a new header file, move the bochs vbe dispi interface
defines to it, so they can be used outside vga code.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-id: 20180522165058.15404-2-kraxel@redhat.com