Add smu_v11_0_get_power_limit function to get power limit vaule.

v2: update "set" to "get", it only implements "get" behavior. (Alex)
Signed-off-by: NLikun Gao <Likun.Gao@amd.com>
Reviewed-by: NHuang Rui <ray.huang@amd.com>
Acked-by: NAlex Deucher <alexander.deucher@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>