Audio HAL: More generalization for types imports

Complement imports of audio::CPP_VERSION with audio::common::CPP_VERSION
for core.

Import namespaces in VTS tests.

Remove "using namespace" from .cpp files where there
are already imports in the .h file.

Test: try moving types between audio/types.hal and common/types.hal.
Change-Id: I49c2e2466c8175f2516c2273f5c26d125afd4801