drm/amdgpu: always register an MMU notifier for userptr

stable inclusion
from stable-v5.10.157
commit feb97cf45e77ec7dfec56a3e1f0a1c8763f286ff
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I7MU59

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=feb97cf45e77ec7dfec56a3e1f0a1c8763f286ff



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commit b39df63b upstream.

Since switching to HMM we always need that because we no longer grab
references to the pages.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Acked-by: Felix Kuehling <Felix.Kuehling@amd.com>
CC: stable@vger.kernel.org
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: sanglipeng <sanglipeng1@jd.com>