Add a model of Xilinx Versal's OSPI flash memory controller.

Signed-off-by: Francisco Iglesias <francisco.iglesias@xilinx.com>
Reviewed-by: Luc Michel <luc@lmichel.fr>
Message-id: 20220121161141.14389-7-francisco.iglesias@xilinx.com
[PMM: fixed indent]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>