configs: add audio vendor product mk file

Copy audio specific defs and rules from vendor-specific
target makefiles (base.mk, msmnile_au.mk, msmsteppe_au.mk)
to audio owned makefile. All the future audio vendor product
defs and rules will be configured in the audio_vendor_product.
The softlink for audio_vendor_product.mk was created in
vendor/qcom/defs/product-defs/vendor/ .

Change-Id: If6477fbc4d287ca6ad079451a61e84cf07d4e126