Turn the SD card into a QOM device.
This conversion only changes the device itself; the various
functions which are effectively methods on the device are not
touched at this point.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Peter Crosthwaite <crosthwaite.peter@gmail.com>
Reviewed-by: Alistair Francis <alistair.francis@xilinx.com>
Message-id: 1455646193-13238-3-git-send-email-peter.maydell@linaro.org