kernel: Disable CONFIG_DEBUG_FS

kernel: Disable CONFIG_DEBUG_FS

According to the kernel's documentation,

> debugfs is a virtual file system that kernel developers use to put
> debugging files into. Enable this option to be able to read and
> write to these files.

There is no legitimate reason why one has to do so on an IPFire machine.
Further, the vast debugging options (i.e. related to various drivers)
have never been enabled, limiting the use of this virtual file system
even further.

This patch therefore proposes to disable it entirely, since its
potential security impact outweights its benefits. Due to operational
constraints, changes to ARM kernel configurations will be made if this
patch is approved for x86_64.

Signed-off-by: Peter Müller <peter.mueller@ipfire.org>
Reviewed-by: Michael Tremer <michael.tremer@ipfire.org>