drm/amdgpu: extend PSP FW loading support to 8 SDMA instances

Arcturus has 8 instances of SDMA.  Update host to PSP interface
to handle it.

Signed-off-by: John Clements <john.clements@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>