linuxkpi: Add `pin_user_pages*()` functions

[dumbbell]

Summary

They were defined in the i915 DRM driver. I move the code in linuxkpi so it can benefit other drivers.

This is part of the update of the DRM drivers to Linux 5.13.

[manu]

This alone will need some tweak for drm-kmod separated from the update to 5.13 (so for both master and 5.10-lts based on a __FreeBSD_version bump). Can you prepare a PR on github ?

[dumbbell]

In D38078#867364, @manu wrote:

This alone will need some tweak for drm-kmod separated from the update to 5.13 (so for both master and 5.10-lts based on a __FreeBSD_version bump). Can you prepare a PR on github ?

Both branches continues to build just fine. Do you think it's still required?

[manu]

In D38078#868242, @dumbbell wrote:

In D38078#867364, @manu wrote:

This alone will need some tweak for drm-kmod separated from the update to 5.13 (so for both master and 5.10-lts based on a __FreeBSD_version bump). Can you prepare a PR on github ?

Both branches continues to build just fine. Do you think it's still required?

If everything works I'm fine with this then.