drm/amdgpu/swsmu: handle manual fan readback on SMU11

Need to read back from registers for manual mode rather than
using the metrics table.

Bug: https://gitlab.freedesktop.org/drm/amd/-/issues/1164


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