wandboard: add Future Eletronics 7" WVGA LCD extension board

This adds support for the 7" WVGA produced by Future Eletronics and
make it dynamically detect if it is connected or not based on the
touchscreen controller.

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
Acked-by: Stefano Babic <sbabic@denx.de>