mei: add per device configuration

Add mei_cfg structure that holds per device configuration
data and hooks, as the first step we add firmware
status register offsets

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