libaudiohal: Add support for audio@7.1

Added libauiohal@7.1 to support audio@7.1, core interfaces only,
no effects (these are still @7.0). Removed version-bound
namespace from the implementation to simplify code reuse. The
implementation classes are not exported from the libaudiohal
.so, thus no name conflicts could occur.

libaudiohal now tries audio@7.1 first and loads libaudiohal@7.1
client library. The library code has been updated to handle
opening of the primary device in the way appropriate for V7.1.

Note that as the effect HAL is 7.0, libaudiohal ends up loading
@7.1 client for the core HAL and @7.0 client for the effect
HAL. This can increase memory consumption.

Bug: 214426419
Test: check audio functionality on cuttlefish
      and redfin (temporarily updated to @7.1)
Change-Id: I62f72dc86dee472d6b358a9861882b9b7f6c6177