Enable kvm emulated watchdog

Enable kvm emulated watchdog

Enable the KVM emulated watchdog if KVM supports (use the
capability enablement in watchdog handler). Also watchdog exit
(KVM_EXIT_WATCHDOG) handling is added.
Watchdog state machine is cleared whenever VM state changes to running.
This is to handle the cases like return from debug halt etc.

Signed-off-by: Bharat Bhushan <[email protected]>
[agraf: rebase to current code base, fix non-kvm cases]
Signed-off-by: Alexander Graf <[email protected]>