powerpc/selftests: Use gettid() instead of getppid() for null_syscall

gettid() is 10% lighter than getppid(), use it for null_syscall selftest.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/0ad62673d3e063f848e7c99d719bb966efd433e8.1622809833.git.christophe.leroy@csgroup.eu

treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152

Based on 1 normalized pattern(s):

this program is free software you can redistribute it and or modify
it under the terms of the gnu general public license as published by
the free software foundation either version 2 of the license or at
your option any later version

extracted by the scancode license scanner the SPDX license identifier

GPL-2.0-or-later

has been chosen to replace the boilerplate/reference in 3029 file(s).

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Allison Randal <allison@lohutok.net>
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190527070032.746973796@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

powerpc/selftest: fix type of mftb() in null_syscall

All callers of mftb() expect 'unsigned long', and the function itself
only returns lower part of the TB so it really is 'unsigned long'
not 'unsigned long long'

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

selftests/powerpc: Add Anton's null_syscall benchmark to the selftests

Pull in a version of Anton's null_syscall benchmark:
http://ozlabs.org/~anton/junkcode/null_syscall.c

Suggested-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Anton Blanchard <anton@au.ibm.com>
Signed-off-by: Rui Teng <rui.teng@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>