drm/amd/pm: Fetch current power limit from PMFW

On SMU v13.0.12, always query the firmware to get the current power
limit as it could be updated through other means also.

Signed-off-by: Lijo Lazar <lijo.lazar@amd.com>
Reviewed-by: Asad Kamal <asad.kamal@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>