hw/i2c-ddc.c: Implement DDC I2C slave

hw/i2c-ddc.c: Implement DDC I2C slave

Implement an I2C slave which implements DDC and returns the
EDID data for an attached monitor.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@xilinx.com>
Tested-by: Hyun Kwon <hyun.kwon@xilinx.com>
Signed-off-by: KONRAD Frederic <fred.konrad@greensocs.com>
Message-id: 1465833014-21982-7-git-send-email-fred.konrad@greensocs.com

  - Rebased on the current master.
  - Modified for QOM.

Signed-off-by: KONRAD Frederic <fred.konrad@greensocs.com>
Reviewed-by: Alistair Francis <alistair.francis@xilinx.com>
Tested-By: Hyun Kwon <hyun.kwon@xilinx.com>
[PMM: actually wire up the vmstate to dc->vmsd]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>