PPC: e500: advertise 4.2 MPIC only if KVM supports EPR

Older KVM versions don't support EPR which breaks guests when we announce
MPIC variants that support EPR.

Catch that case and expose only MPIC version 2.0 which tells the guest that
we don't support the EPR capability yet.

Signed-off-by: Stuart Yoder <stuart.yoder@freescale.com>
[agraf: Add comment, route cap check through kvm_ppc.c]
Signed-off-by: Alexander Graf <agraf@suse.de>
PPC: Remove env->hreset_excp_prefix

This value is not needed if we use correctly the MSR[IP] bit.

excp_prefix is always 0x00000000, except when the MSR[IP] bit is
implemented and set to 1, in that case excp_prefix is 0xfff00000.

The handling of MSR[IP] was already implemented but not used at reset
because the value of env->msr was changed "manually".

The patch uses the function hreg_store_msr() to set env->msr, this
ensures a good handling of MSR[IP] at reset, and therefore a good value
for excp_prefix.

Signed-off-by: Fabien Chouteau <chouteau@adacore.com>
Signed-off-by: Alexander Graf <agraf@suse.de>
target-ppc: fix nego and subf*o instructions

The overflow computation of nego and subf*o instructions has been broken
in commit ffe30937. Contrary to other targets, the instruction is subtract
from an not subtract on PowerPC.

This patch fixes the issue by using the correct argument in the xor
computation. Thanks to Peter Maydell for the hint.

With this change the PPC emulation passes the Gwenole Beauchesne
testsuite again.

Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Alexander Graf <agraf@suse.de>