imx-alsa-plugins: new package

imx-alsa-plugins: new package

Freescale specific alsa-lib plugins for the i.MX processor family.

For now, the only provided plugin is:
  * Rate Converter Plugin Using Freescale ASRC Resampler

The ASRC hardware resampler can be found on i.MX53 and most i.MX 6
processors.

Signed-off-by: Jörg Krause <joerg.krause@embedded.rocks>
[Thomas:
 - Remove the mention "This package is provided by Freescale as-is and
   doesn't have an upstream." from the Config.in help text, since
   according to Gary Bisson, there is a Git repository for such
   projects, and therefore some form of upstream.
 - Add missing entry to DEVELOPERS file.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>