lscpu: slightly correct iSeries and pSeries detection

According to Alexander Graf's comments on util-linux@vger.kernel.org.
Maybe we would need to add some more code to detect pSeries emulated
by Qemu/KVM.

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>
tests: add lscpu IBM pSeries test data

Just adding missing files
  /proc/device-tree/ibm,partition-name
  /proc/device-tree/hmc-managed?
to our existing lscpu-ppc64-POWER7-64cpu dump.

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>