drm/amdgpu/swsmu: use percent rather than rpm for manual fan control (v2)

On some boards the rpm interface apparently does not work at all
leading to the fan not spinning or spinning at strange speeds.
Both interfaces work properly on the boards I have.
Let's try and use the percent interface instead.

v2: rebase on revert

Bug: https://gitlab.freedesktop.org/drm/amd/-/issues/1408


Reviewed-by: Evan Quan <evan.quan@amd.com> (v1)
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>