ASoC: dmic: add DT module alias

Before this patch the only alias provided by the dmic module is:
alias:          platform:dmic-codec

Device instantiated from DT will not probe automatically with this

After this patch, here is the new alias list:
alias:          platform:dmic-codec
alias:          of:N*T*Cdmic-codecC*
alias:          of:N*T*Cdmic-codec

Now the dmic codec probes automatically when instantiated from DT.

Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Mark Brown <broonie@kernel.org>