ASoC: ux500: drop clock gating widgets from machine driver

Drop ab8500 clock gating widgets from mop500_ab8500_ctrls, as these bits
are already controlled by ab8500 codec driver and should not be exposed
to the user.

Signed-off-by: Fabio Baltieri <fabio.baltieri@linaro.org>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>