mei: drop amthif internal client

AMTHIF has special support in the mei drive, it handles multiplexing
multiple user space connection above single me client connection.
Since there is no additional addressing information there is a strict
requirement on the traffic order on each connection and on the "read
after write" order within the connection. This creates a lot of
complexity mostly because the other client types do not necessarily fall
under the same restriction.    After carefully studying the use of the
AMTHIF client, we came to conclusion that the multiplexing is not really
utilized by any application and we may safely remove that support and
significantly simplify the driver.

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>