lindebugfs: Add missing debugfs_create_u*() and debugfs_create_x*()

The debugfs_create_x*() variants are the same as their
debugfs_create_u*() equivalent, but they work with lowercase
hexadecimal.

While here, fix a few style(9) issues.

Reviewed by: manu
Approved by: manu
Differential Revision: https://reviews.freebsd.org/D38087