cpu: flush TB cache when loading VMState

Flushing TB cache is required because TBs key in the cache may match
different code which existed in the previous state.

Signed-off-by: Pavel Dovgalyuk <pavel.dovgaluk@ispras.ru>
Signed-off-by: Maria Klimushenkova <maria.klimushenkova@ispras.ru>
Message-Id: <20180110134846.12940.99993.stgit@pasha-VirtualBox>
[Add comment suggested by Peter Maydell. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>