drm/amd/powerplay: unified VRAM address for driver table interaction with SMU V2

By this, we can avoid to pass in the VRAM address on every table
transferring. That puts extra unnecessary traffics on SMU on
some cases(e.g. polling the amdgpu_pm_info sysfs interface).

V2: document what the driver table is for and how it works

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>