drm/amdgpu: Disable sysfs pwm1 if not in manual fan control

Following lm-sensors 3.0.0,
Only enable pwm1 sysfs when fan control mode(pwm1_enable)
in manual

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