linuxkpi: Add sysfs_create_link() in <linux/sysfs.h>

[Why]
The amdgpu DRM driver started to use it in Linux 5.18.

[How]
The function is a no-op as I'm not sure how to implement this with
sysctls yet.

Reviewed by: manu
Approved by: manu
Differential Revision: https://reviews.freebsd.org/D43022