drm/radeon: fix pm handling in radeon_gpu_reset

pm_suspend is handled in the radeon_suspend callbacks.
pm_resume has special handling depending on whether
dpm or legacy pm is enabled.  Change radeon_gpu_reset
to mirror the behavior in the suspend and resume
pathes.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Cc: stable@vger.kernel.org