drm/amdgpu: set firmware loading type as direct by default for raven

In previous case, driver can't enable psp via the kernel parameter for raven.
We should open this path and set it as direct by default till psp firmware
loading is workable.

Signed-off-by: Huang Rui <ray.huang@amd.com>
Reviewed-by: Junwei Zhang <Jerry.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>