wm8962: Expose DMIC_ENA, ADCL_ENA and ADCR_ENA as ALSA controls

In order to be able to use the analog microphone input from the headphone jack, digital microphones need to be disabled in the codec. However, currently there's no way to do it - the driver automatically sets DMIC_ENA as part of its power management routines.

The ideal scenario would be to still have the driver enable and disable DMIC_ENA automatically for power savings, but only when an appropriate ALSA mixer control is enabled - so the headset UCM device can leave it disabled.

(register WM8962_PWR_MGMT_1 [0x19], bit WM8962_DMIC_ENA_SHIFT [10])

Related to #5 (closed)