add debugfs interface amdgpu_force_sclk
to set arbitrary sclk for navi14

v2: Add lock
Signed-off-by: NChengming Gui <Jack.Gui@amd.com>
Reviewed-by: NEvan Quan <evan.quan@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>