video: vgacon: Don't build on arm64

commit ee23794b

 upstream.

arm64 is unlikely to have a VGA console and does not export screen_info
causing build failures if the driver is build, for example in all*config.
Add a dependency on !ARM64 to prevent this.

This list is getting quite long, it may be easier to depend on a symbol
which architectures that do support the driver can select.

Signed-off-by: Mark Brown <broonie@linaro.org>
[tomi.valkeinen@ti.com: moved && to first modified line]
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>