Add IIR2 filter interface for the wcd9304 codec. Control the two 5 band IIR filters in the audio codec through mixer controls. Enable individual IIR filter bands and set band coefficients. Change the IIR filter code to use snd_soc_write instead of snd_soc_update_bits. If update bits is used the IIR registers may not be correctly updated. Change-Id: I92fc147641e9eb270d8176f20445371fe5cc2f92 Signed-off-by: Asish Bhattacharya <asishb@codeaurora.org>