eventfs: Implement eventfs dir creation functions

Add eventfs_file structure which will hold the properties of the eventfs
files and directories.

Add following functions to create the directories in eventfs:

eventfs_create_events_dir() will create the top level "events" directory
within the tracefs file system.

eventfs_add_subsystem_dir() creates an eventfs_file descriptor with the
given name of the subsystem.

eventfs_add_dir() creates an eventfs_file descriptor with the given name of
the directory and attached to a eventfs_file of a subsystem.

Add tracefs_inode structure to hold the inodes, flags and pointers to
private data used by eventfs.

Link: https://lkml.kernel.org/r/1690568452-46553-5-git-send-email-akaher@vmware.com

Signed-off-by: Ajay Kaher <akaher@vmware.com>
Co-developed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Tested-by: Ching-lin Yu <chinglinyu@google.com>
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202305051619.9a469a9a-yujie.liu@intel.com
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

treewide: Add SPDX license identifier - Makefile/Kconfig

Add SPDX license identifiers to all Make/Kconfig files which:

- Have no license information of any form

These files fall under the project license, GPL v2 only. The resulting SPDX
license identifier is:

GPL-2.0-only

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

tracefs: Add new tracefs file system

Add a separate file system to handle the tracing directory. Currently it
is part of debugfs, but that is starting to show its limits.

One thing is that in order to access the tracing infrastructure, you need
to mount debugfs. As that includes debugging from all sorts of sub systems
in the kernel, it is not considered advisable to mount such an all
encompassing debugging system.

Having the tracing system in its own file systems gives access to the
tracing sub system without needing to include all other systems.

Another problem with tracing using the debugfs system is that the
instances use mkdir to create sub buffers. debugfs does not support mkdir
from userspace so to implement it, special hacks were used. By controlling
the file system that the tracing infrastructure uses, this can be properly
done without hacks.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>