mfd: wcd9xxx: Add support for MAD specific DMIC clk rate

MAD (Microphone Activity Detection) block on the codec can use
different Digital MIC (DMIC) clock rate as compared to regular audio
recording use cases. Add support to configure DMIC clock rate specific
to MAD which will be used by codec drivers whenever MAD is active.

CRs-fixed: 692015
Change-Id: Ife73a407c8d1a2d16b9b89df4979395a575f96c2
Signed-off-by: Bhalchandra Gajare <gajare@codeaurora.org>