drm/amdgpu: Add fan RPM setting via sysfs

Add fan1_target for get/set fan speed in RPM unit
Add fan1_min/fan1_max for get min, max fan speed in RPM unit
Add fan1_enable to enable/disable the fan1 sensor

v3: drop the hardcode value of min/max rpm in comments pointed
    out by Alex.
v2: query the min/max rpm gpu support instand of hardcode value.

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>