drm/amd/powerplay: clear the swSMU code layer

With this cleanup, the APIs from amdgpu_smu.c will map to
ASIC specific ones directly. Those can be shared around
all SMU V11/V12 ASICs will be put in smu_v11_0.c and
smu_v12_0.c respectively.

Signed-off-by: Evan Quan <evan.quan@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>