This patch adds the stm32f2xx System Configuration
Controller. This is used to configure what memory is mapped
at address 0 (although that is not supported) as well
as configure how the EXTI interrupts work (also not
supported at the moment).

This device is not required for basic examples, but more
complex systems will require it (as well as the EXTI device)
Signed-off-by: NAlistair Francis <alistair@alistair23.me>
Reviewed-by: NPeter Crosthwaite <peter.crosthwaite@xilinx.com>
Message-id: 5d499d7b60b61d5d6dcb310b2e55411b1f53794e.1424175342.git.alistair@alistair23.me
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>