Move nvidia driver installer to /usr partition

[pothos]

Current situation

The nvidia driver installer is part of the OEM tools for Azure and AWS EC2.
Work was started in flatcar-archive/coreos-overlay#2480 to move it to the /usr partition but not yet finished.
The nvidia driver installer is not part of the Azure sysext.

Impact

Before we branch the next Alpha we should complete the move to /usr.

Implementation

Port the old proposed changes to the new scripts repo.

Future

We also migrate the old instances by writing to the migration marker file from the update-engine post-install hook when migrating a machine from the old OEM partition contents to the new sysext image content.

/etc/systemd/system/nvidia.service
/oem/bin/setup-nvidia
/oem/bin/install-nvidia
/oem/units/nvidia.service