configs: qssi: add audio system product mk file

as part of audio self-containment, created a
audio_system_product.mk file where audio related 
product system defs can be configured in this file.

the softlink for this will be created in
vendor/qcom/defs/product-defs/system/ .

Change-Id: Ief3a0a4544511ed3106c333fe4cdb7eb105a0138