drm/amdgpu: invalidate L2 before SDMA IBs (v2)

This fixes GPU hangs due to cache coherency issues.

v2: Split the version bump to a separate patch

Signed-off-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Tested-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org