drm/amd/powerplay: add the smu manager for vega20 (v2)

The SMU manager handles the driver interaction with the SMU
which handles clock and voltage controls.

v2: switch to SOC15 register access macros
    reserve space for ActivityMonitor table
    enable SMU fw loading
    Drop dead code from bringup

Signed-off-by: Evan Quan <evan.quan@amd.com>
Reviewed-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>