mei: add a spin lock to protect rd_completed queue

In order to support vtags we need to access read completed
queue out of driver big lock.
Add a spin lock to protect rd_completed queue.

Signed-off-by: Alexander Usyskin <alexander.usyskin@intel.com>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Link: https://lore.kernel.org/r/20200818115147.2567012-7-tomas.winkler@intel.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>