powerpc/64s: Wire up cpu_show_spectre_v1()

commit 56986016cb8cd9050e601831fe89f332b4e3c46e upstream.

Add a definition for cpu_show_spectre_v1() to override the generic
version. Currently this just prints "Not affected" or "Vulnerable"
based on the firmware flag.

Although the kernel does have array_index_nospec() in a few places, we
haven't yet audited all the powerpc code to see where it's necessary,
so for now we don't list that as a mitigation.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>