drm/amd/pm: add smu power_limit callback for smu_v13_0_7

- get_power_limit
- set_power_limit

add above callback functions to enable power_cap hwmon node.

Signed-off-by: Yang Wang <KevinYang.Wang@amd.com>
Reviewed-by: Kenneth Feng <kenneth.feng@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>