drm/amdgpu: register gpu instance before fan boost feature enablment

Otherwise, the feature enablement will be skipped due to wrong count.

Fixes: beff74bc ("drm/amdgpu: fix a race in GPU reset with IB test (v2)")
Signed-off-by: Evan Quan <evan.quan@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>