ASoC: rockchip: add support for pdm controller

The Pulse Density Modulation Interface Controller (PDMC) is
a PDM interface controller and decoder that support PDM format.
It integrates a clock generator driving the PDM microphone
and embeds filters which decimate the incoming bit stream to
obtain most common audio rates.

Signed-off-by: Sugar Zhang <sugar.zhang@rock-chips.com>
Signed-off-by: Mark Brown <broonie@kernel.org>