drm/amdgpu: Set vega20 load_type to AMDGPU_FW_LOAD_DIRECT.

Please revert this patch when psp load fw is enabled.

Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Feifei Xu <Feifei.Xu@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>