mei: bus: add more client attributes to sysfs

mei: bus: add more client attributes to sysfs

Export more client attributes via sysfs that are usually obtained
upon connection. In some cases, for example a monitoring application
may wish to know the attributes without actually performing the connection.
Added attributes:
max number of connections, fixed address, max message length.

Signed-off-by: Alexander Usyskin <alexander.usyskin@intel.com>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Link: https://lore.kernel.org/r/20191116142136.17535-1-tomas.winkler@intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>