mei: revamp client disconnection flow

Split disconnected state into two parts first reception disconnect
response from the firmware and second actually setting of disconnected
state.  Book keeping data are needed for processing and after firmware
disconnected the client and are cleaned when setting the disconnected
state in mei_cl_set_disconneted() function.
Add mei_cl_send_disconnect to reduce code duplication.

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Alexander Usyskin <alexander.usyskin@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>