ASoC: bells: Select WM1250-EV1 Springbank audio I/O module

Ensure we select the WM1250-EV1 as the current software system
configuration demands it.

Signed-off-by: Dimitris Papastamos <dp@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>