audio.common@2.0-util: vendor_available + in Soong

vendor_available: separate copy built on the vendor partition for
BOARD_VNDK_VERSION := current devices.

**************************************************
See full implications + warning on:
https://android-review.googlesource.com/#/c/369995/

(Ia4eb5378d941033b07673daf682e66051cd3c075)
***************************************************

Test: (sanity) audio works on internal marlin
Test: (sanity) hangouts call on internal marlin
Test: warnings don't show up on BOARD_VNDK_VERSION := current devices.
Bug: 33241851

Change-Id: I2de1b789a44d238e31108312b4ec0dd5d404b1e6