drm/amdgpu: refuse to reserve io mem for split VRAM buffers

[ Upstream commit 4694335dad7357e9b3d7822ab13049014d74d8b0 ]

When the fast blit path fails while attempting to move a buffer from RAM
to VRAM, we fall back to a CPU-based memcpy that cannot handle split VRAM
buffers. Instead of crashing, simply fail the buffer move.

Ideally, we would teach TTM about split buffers so that the fallback still
works in this case, but that is quite involved. So for now, apply the
simplest possible fix.

Fixes: 40361bb1704b ("drm/amdgpu: add VRAM manager v2")
Signed-off-by: Nicolai Hähnle <nicolai.haehnle@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>