drm/amdgpu: add lock in amdgpu_gart_invalidate_tlb

We need to take the reset domain lock before flush hdp. We can't put the
lock inside amdgpu_device_flush_hdp itself because it is used during
reset where we already take the write side lock.

Signed-off-by: Yunxiang Li <Yunxiang.Li@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>