drm/amd/amdgpu: adjust the fw load type list

Use 0 for legacy backdoor and 1 for frontdoor.

Signed-off-by: Chengming Gui <Jack.Gui@amd.com>
Reviewed-by: Likun Gao <Likun.Gao@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>