exec: add cpu_synchronize_state to cpu_memory_rw_debug

exec: add cpu_synchronize_state to cpu_memory_rw_debug

I sometimes got "Cannot access memory" when using the x command
on the monitor. Turns out that the cpu env did contain stale data
(e.g. wrong control register content for page table origin).
We must synchronize the state of the CPU before walking the page
tables. A similar issues happens for a remote gdb, so lets
do the cpu_synchronize_state in cpu_memory_rw_debug.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Message-Id: <1488896348-13560-1-git-send-email-borntraeger@de.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>