drm/amdgpu: Enable SA software trap.

Enables support for software trap for MES >= 4.
Adapted from implementation from Jay Cornwall.

v2: Add IP version check in conditions.
v3: Remove debugger code changes.

Signed-off-by: Jay Cornwall <Jay.Cornwall@amd.com>
Signed-off-by: David Belanger <david.belanger@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>