target-ppc: Remove POWER7+ and POWER8E families

POWER8E is architecturally equal to POWER8 and POWER7+ is equal to
POWER7. Also no user space tool makes any difference for CPU node name
in the device tree (such as PowerPC,POWER7@0 vs. PowerPC,POWER7+@0).
So there is no point in emulating POWER7+ and POWER8E apart from POWER7
and POWER8. Also, the previos patch implemented multiple PVR mask support
per CPU class so POWER7 class now covers both POWER7 and POWER7+ CPUs,
same is valid for POWER8/8E.

This removes POWER7+ and POWER8E classes. This replaces references
to POWER7P/POWER8E families with POWER7/POWER8 families.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Alexander Graf <agraf@suse.de>
