drm/amdgpu: Clear HDP_MISC_CNTL.HDP_FLUSH_INVALIDATE_CACHE

So that we can invalidate and flush the HDP independently

Signed-off-by: Chunming Zhou <David1.Zhou@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>