linuxkpi: Add <linux/limits.h>

[dumbbell]

Summary

For now, it's empty. It is included by the DRM drivers but nothing is missing otherwise. Perhaps something we already defined should be in limits.h instead of another header.

This is part of the update of the DRM drivers to Linux 5.14.

[manu]

If it's empty this should go to the dummy directory and when we add stuff in it we will then move it.

[dumbbell]

Address @manu comment and add header under dummy.