kvm: Add missing bits to support live migration

kvm: Add missing bits to support live migration

This patch adds the missing hooks to allow live migration in KVM mode.
It adds proper synchronization before/after saving/restoring the VCPU
states (note: PPC is untested), hooks into
cpu_physical_memory_set_dirty_tracking() to enable dirty memory logging
at KVM level, and synchronizes that drity log into QEMU's view before
running ram_live_save().

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>