staging: most: aim-sound: add flexible format support

Currently, the only supported PCM formats are 1x8", "2x16", "2x24",
"2x32" or "6x16".

This adds support for the format "Nx{8,16,24,32}" that also includes the
exotic PCM formats like "4x16", "5x8", etc.

Signed-off-by: Andrey Shvetsov <andrey.shvetsov@k2l.de>
Signed-off-by: Christian Gromm <christian.gromm@microchip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>