drm/amdgpu/vpe: fix vpe dpm setup failed

The vpe dpm settings should be done before firmware is loaded.
Otherwise, the frequency cannot be successfully raised.

Signed-off-by: Peyton Lee <peytolee@amd.com>
Reviewed-by: Lang Yu <lang.yu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>