Enable HAVE_ARCH_KCSAN on all powerpc platforms, permitting use of the
kernel concurrency sanitiser through the CONFIG_KCSAN_* kconfig options.

Boots and passes selftests on 32-bit and 64-bit platforms. See
documentation in Documentation/dev-tools/kcsan.rst for more information.
Signed-off-by: Rohan McLure <rmclure@linux.ibm.com>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Acked-by: Marco Elver <elver@google.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/1a1138966780c3709f55bde8a0eb80209fa4395d.1683892665.git.christophe.leroy@csgroup.eu