i2c: Factor our send() and recv() common logic

Most of the control flow logic between send and recv (error checking
etc) is the same. Factor this out into a common send_recv() API.
This is then usable by clients, where the control logic for send
and receive differs only by a boolean. E.g.

if (send)
   i2c_send(...):
else
   i2c_recv(...);

becomes:

i2c_send_recv(... , send);

Signed-off-by: Peter Crosthwaite <crosthwaite.peter@gmail.com>
Reviewed-by: Alistair Francis <alistair.francis@xilinx.com>
Signed-off-by: KONRAD Frederic <fred.konrad@greensocs.com>
Message-id: 1465833014-21982-4-git-send-email-fred.konrad@greensocs.com
Changes from FK:
  * Rebased on master.
  * Rebased on my i2c broadcast patch.
Signed-off-by: KONRAD Frederic <fred.konrad@greensocs.com>
Reviewed-by: Alistair Francis <alistair.francis@xilinx.com>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
