target-s390x: Migrate to new NMI interface

This implements an NMI interface for s390 and s390-ccw machines.

This removes #ifdef s390 branch in qmp_inject_nmi so new s390's
nmi_monitor_handler() callback is going to be used for NMI.

Since nmi_monitor_handler()-calling code is platform independent,
CPUState::cpu_index is used instead of S390CPU::env.cpu_num.
There should not be any change in behaviour as both @cpu_index and
@cpu_num are global CPU numbers.

Also, s390_cpu_restart() takes care of preforming operations in
the specific CPU thread so no extra measure is required here either.

Since the only error s390_cpu_restart() can return is ENOSYS, convert
it to QERR_UNSUPPORTED.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
---
Changes:
v7:
* since now s390' are QOM'ed, add interface to them and do not create
new object

v6:
* supported NMI interface

v5:
* added ENOSYS -> QERR_UNSUPPORTED, qapi/qmp/qerror.h was added for this

v4:
* s/\<nmi\>/nmi_monitor_handler/

v3:
* now contains both old code removal and new code insertion, easier to
track changes

Conflicts:
	hw/s390x/s390-virtio.c
target-i386: Migrate to new NMI interface

This implements an NMI interface for i386 PC machines.

This removes #ifdef I386 branch in qmp_inject_nmi so new i386's nmi()
callback is going to be used for NMI.

This changes code to inject NMI on the current CPU instead of injecting
it on every CPU. However that does not seem to be an issue.

Since kvm_apic_external_nmi() takes care of preforming operations in
the specific CPU thread so no extra measure is required here.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
---
Changes:
v6:
* make use of NMI interface

v5:
* make use of NMI interface

v4:
* s/\<nmi\>/nmi_monitor_handler/

v3:
* now contains both old code removal and new code insertion, easier to
track changes
* fixed compile for linux-user
target-ppc: Add support for new NMI interface

This implements an NMI interface POWERPC SPAPR machine.
This enables an "nmi" HMP/QMP command supported on SPAPR.

This calls POWERPC_EXCP_RESET (vector 0x100) in the guest to deliver NMI
to every CPU. The expected result is XMON (in-kernel debugger) invocation.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
---
Changes:
v6:
* support NMI interface

v4:
* s/\<nmi\>/nmi_monitor_handler/
* added note about XMON into commit log

v3:
* ppc_cpu_do_nmi() is exported from excp_helper.c instead of powerpc_excp()