introduce a new qom device to deal with panicked event

introduce a new qom device to deal with panicked event

pvpanic device is used to send guest panic event from guest to qemu.

When guest panic happens, pvpanic device driver will write a event
number to IO port 0x505(which is the IO port occupied by pvpanic device,
by default). On receiving the event, pvpanic device will pause guest
cpu(s), and send a qmp event QEVENT_GUEST_PANICKED.

Signed-off-by: Wen Congyang <[email protected]>
Signed-off-by: Hu Tao <[email protected]>
Reviewed-by: Markus Armbruster <[email protected]>
Message-id: b66077a40235b3531632a05a6ff373850afc7d2e.1366945969[email protected]
Signed-off-by: Anthony Liguori <[email protected]>