mei: add support for mei extended header.

mei: add support for mei extended header.

Add an extend header beyond existing 4 bytes of the mei message header.
The extension is of variable length, starting with meta header
that contains the number of headers and the overall size of
the extended headers excluding meta header itself followed by
TLV list of extended headers. Currently only supported extension is
the vtag. From the HW perspective the extended headers is already
part of the payload.

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Alexander Usyskin <alexander.usyskin@intel.com>
Link: https://lore.kernel.org/r/20200818115147.2567012-5-tomas.winkler@intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>