drm/amd/pm: modify the power limit level parameter from bool to enum type

The original smu_get_power_limit callback accepts the power limit level
parameter as bool which limits to max and current. For possible needs to
retrieve other level like min, extend the parameter type using enum.

Signed-off-by: Xiaomeng Hou <Xiaomeng.Hou@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>