branches: 1.1.2;
Introduce new example kernel module: panic_string

The panic_string module accepts input from a device file over the write(2)
system call.

It prints panic(9) message passed from user space, e.g.:

echo "Hello world" > /dev/panic

If a string is empty or contain only whitespaces it's ignored and panic(9)
is not triggered. If a non printable character is passed within the input
buffer, the rest of the string is ignored.

This module performs the sync(8) operation before panic(9) to flush cache.

Submitted by Harry Pantazis.
Simplified and cleaned up by myself.