ASoC: twl6040: Enable plug detection interrupts

Enable plug detection interrupt mask in order to get headset
PLUGINT/UNPLUGINT interrupts.

Signed-off-by: Misael Lopez Cruz <misael.lopez@ti.com>
Signed-off-by: Margarita Olaya Cabrera <magi.olaya@ti.com>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>