ASoC: TWL4030: Enable/disable voice digital filters

Enable TWL4030 VTXL/VTXR and VRX digital filters for uplink
and downlink paths, respectively.

This patch also corrects voice 8/16kHz mode selection bit
(SEL_16K) of CODEC_MODE register.

Signed-off-by: Misael Lopez Cruz <x0052729@ti.com>
Acked-by: Peter Ujfalusi <peter.ujfalusi@nokia.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>