drm/radeon/dpm: switch on new late_enable callback

Right now it's called right after enable, but after
reworking the dpm init order, it will get called later
to accomodate loading the smc early, but enabling
thermal interrupts and block powergating later after
the ring tests are complete.

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