Add the STM32F2xx SPI device.

Signed-off-by: Alistair Francis <alistair@alistair23.me>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 8197811d5c94f814fa67c6a33ca2f7fd0aa97432.1474742262.git.alistair@alistair23.me
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>