Create a new sound card to access MICFIL based on rpmsg channel

Merge series from Chancel Liu <chancel.liu@nxp.com>:

At a previous time, we have successfully created a virtual sound card
based on rpmsg. The sound card works under this mechanism Cortex-A core
tells the Cortex-M core the format, rate, channel, .etc configuration
of the PCM parameters and Cortex-M controls real hardware devices such
as SAI and DMA. From the view of Linux side, the sound card is bound to
a rpmsg channel through which it can access SAI.

Here these patches are introduced to create a new virtual sound card to
access MICFIL based on a new created rpmsg channel. It's easy to create
a new rpmsg channel for MICFIL through rpmsg name service announcment.
Also the other ASoC components bound to this rpmsg MICFIL sound card
will be registered with these patches.

If other sound cards using different hardware devices needs to be
created over rpmsg in the future, these patches can be referred.