drm/radeon: set speaker allocation for DCE4/5 (v2)

This updates the audio driver to the speaker allocation
block from the EDID.  A similar change was just implemented
for DCE6/8.

v2: remove unused variables

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Acked-by: Rafał Miłecki <zajec5@gmail.com>