drm/amdgpu: Fix atomics on GFX12

If PCIe supports atomics, configure register to prevent DF from
breaking atomics in separate load/store operations.

Signed-off-by: David Belanger <david.belanger@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 666f14cab21b17ccc1bdfe1e82458aa429b3b7e0)