drm/amdgpu: pin the csb buffer on hw init for gfx v8

drm/amdgpu: pin the csb buffer on hw init for gfx v8

[ Upstream commit 72cda9bb5e219aea0f2f62f56ae05198c59022a7 ]

Without this pin, the csb buffer will be filled with inconsistent
data after S3 resume. And that will causes gfx hang on gfxoff
exit since this csb will be executed then.

Signed-off-by: Likun Gao <Likun.Gao@amd.com>
Tested-by: Paul Gover <pmw.gover@yahoo.co.uk>
Reviewed-by: Feifei Xu <Feifei.Xu@amd.com>
Reviewed-by: Xiaojie Yuan <xiaojie.yuan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>