Fix problem with audio policy configuration file.

Having the copy of default audio_policy.conf file in generic_no_telephony.mk
doesn't work because of multiple inheritance on certain products.

Move it to board/generic/device.mk to be consistent with how the audio HAL
modules are managed.

Issue 6333980.

Change-Id: If6053ad596b6f693f43c72ba9cc54cb7a7cfa233