ASoC: wcd9330: Add support for MAD DMIC clk rate

Using lower DMIC clock rates for MAD (Microphone Activity Detection) is
recommended for power saving, whereas the lowest DMIC clock rate that is
allowed depends on the type of on-board microphone. Add support to make
the MAD specific DMIC clock rate configurable.

CRs-fixed: 692015
Change-Id: If271a4ffbe82c91092a32bc4d964cb291bde3caf
Signed-off-by: Bhalchandra Gajare <gajare@codeaurora.org>