Asoc: Add audio backend to hwdep interface

Add audio backend to hwdep interface. This is to provide
ioctl interface to communicate to routing driver.
Currently codec driver uses request_firmware to get calibration data
but as this firmware file is also written by userspace process after
bootup, it is not recommended to use request_firmware. ALSA core
provides mechanism to get hardware dependent data using hwdep nodes.
Codec will use aforementioned nodes to get calibration data from
userspace.
This commit adds hwdep interface for codec calibration.

Change-Id: I7ecdcdb3c16b0b4d232e05f17f44b346ac796fd2
Signed-off-by: Subhash Chandra Bose Naripeddy <snariped@codeaurora.org>
Signed-off-by: Krishnankutty Kolathappilly <kkolat@codeaurora.org>
Signed-off-by: Banajit Goswami <bgoswami@codeaurora.org>
Signed-off-by: Sudheer Papothi <spapothi@codeaurora.org>
Signed-off-by: Meng Wang <mengw@codeaurora.org>