drm/amdgpu: use sdma_v6 single packet invalidation

This achieves the same result as the sequence used in emit_flush_gpu_tlb
but the invalidation is now a single packet instead of the 3 packets
required to implement reg_write_reg_wait.

Signed-off-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Monk Liu <monk.liu@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>