amdgpu/pm: Powerplay API for smu , added get_performance_level

v2: updated the structure name to swsmu_pm_funcs

Modified Functions
  smu_get_performance_level() - modifed arg0 to match Powerplay API get_performance_level

Other Changes
  added a new structure swsmu_dpm_funcs to hold smu functions for Powerplay API
  removed special smu handling from amdgpu_get_power_dpm_force_performance_level

Signed-off-by: Darren Powell <darren.powell@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>