drm/amd/powerplay: support hwmon temperature channel labels V2

Expose temp[1-3]_label hwmon interfaces. While temp2_label
and temp3_label are visible for SOC15 dGPUs only.

- V2: correct temp1_label as "edge"

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