ACPICA: Debugger: Lock namespace for duration of a namespace dump

Prevents issues if the namespace is changing underneath the
debugger.  Especially temporary nodes, since the debugger displays
these also.

Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Lin Ming <ming.m.lin@intel.com>
Reviewed-by: Rafael Wysocki <rjw@sisk.pl>
Signed-off-by: Len Brown <len.brown@intel.com>