drm/radeon/dpm: add smc fan control for SI (v2)

Enable smc fan control for SI boards.  Should
reduce the fan noise on systems with a higher
default fan profile.

v2: disable by default, add rpm controls

bug:
https://bugs.freedesktop.org/show_bug.cgi?id=73338



Signed-off-by: Alex Deucher <alexander.deucher@amd.com>