ASoC: tegra: Add audio mclk parent configuration

Tegra PMC clock clk_out_1 is dedicated for audio mclk from Tegra30
through Tegra210 and currently Tegra clock driver does the initial
parent configuration for audio mclk and keeps it enabled by default.

With the move of PMC clocks from clock driver into PMC driver, audio
clocks parent configuration can be specified through the device tree
using assigned-clock-parents property and audio mclk control should be
taken care of by the audio driver.

This patch has implementation for parent configuration when default
parent configuration through assigned-clock-parents property is not
specified in the device tree.

Tested-by: Dmitry Osipenko <digetx@gmail.com>
Reviewed-by: Dmitry Osipenko <digetx@gmail.com>
Reviewed-by: Sameer Pujar <spujar@nvidia.com>
Signed-off-by: Sowjanya Komatineni <skomatineni@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>