staging/mei: MEI link layer

staging/mei: MEI link layer

Implementation of the communication between host and ME.
connect/disconnect to/from a client, send MEI message,
read MEI message, flow control handling.

Each MEI message has mei_msg_hdr followed by a payload.
Driver is oblivious the payload.

ME Address/ID 	- This is the logical address of the ME
		feature/client of that message.
Host Address/ID	- This is the logical address of the Host
		  client of that message
Length 		- This is the Length of message payload in bytes
Reserved 	-  reserved for future use.
Message Complete - This bit is used to indicative that
		this is the last message of multi message
		MEI transfer of a client message that is larger
		then the MEI circular buffer.
Payload		- Message payload (data) up to 512bytes

The HW data registers are consist two circular buffers,
one for data from ME and other data from Host application.
Each buffer has two pointers, read_ptr (H_CBRP)
and write_ptr (H_CBWP).
The buffers size is defined by depth value that exists
in the status registers (H_CBD and ME_CBD_HRA).
Every read from ME circular buffer cause read_ptr++
Every write to the Host  circular buffer write_ptr++

Flow control MEI message that ME and MEI Driver use to notify
each other that a ME feature/client or Host client buffer is ready
to receive data.

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Itzhak Tzeel-Krupp <itzhak.tzeel-krupp@intel.com>
Signed-off-by: Oren Weil <oren.jer.weil@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>