linuxkpi: Replicate the chain of #include in the cec*.h headers

The i915 DRM driver depends on this namespace pollution to access
debugfs_* functions, after several explicit #include of
<linux/debugfs.h> were removed in Linux 6.10.

Reviewed by: bz, christos
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D54494