drm/amdgpu: Initialize SPM_VMID with 0xf (v2)

SPM_VMID is a global resource, SPM access the video memory according to
SPM_VMID. The initial valude of SPM_VMID is 0 which is used by kernel.
That means UMD can overwrite the memory of VMID0 by enabling SPM, that
is really dangerous.

Initialize SPM_VMID with 0xf, it messes up other user mode process at
most.

v2: squash in indentation fix

Signed-off-by: Jacob He <jacob.he@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>