audio: allow compiling for 64-bit

Fix a few 64-bit warnings and set -Wno-unused-parameter, which makes
the directory warnings-clean on 32-bit and 64-bit.
Remove LOCAL_32_BIT_ONLY.

Change-Id: I688b31683f1a6598419866d9b7b6bc27a7056f4a
Merge "audio: allow compiling for 64-bit"
auto-merger: merge in from aosp/master