linux-user: set ppc64/ppc64le default CPU to POWER8
Set the default to the latest CPU version to have the
largest set of available features.
It is also really needed in little-endian mode because
POWER7 is not really supported in this mode and some distros
(at least debian) generate POWER8 code for their ppc64le target.
Fixes: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=813698 Signed-off-by: Laurent Vivier <lvivier@redhat.com> Reviewed-by: Alexander Graf <agraf@suse.de> Reviewed-by: Michael Tokarev <mjt@tls.msk.ru> Signed-off-by: Riku Voipio <riku.voipio@linaro.org>