drm/amdgpu/gfx10: move update_spm_vmid() out of rlc_init()

rlc_init() is part of sw_init() so it should not touch hardware.
Additionally, calling the rlc update_spm_vmid() callback
directly invokes a gfx on/off cycle which could result in
powergating being enabled before hw init is complete.  Split
update_spm_vmid() into an internal implementation for local
use without gfxoff interaction and then the rlc callback
which includes gfxoff handling.

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