Tidyup the i.MX SoC support by

- Moving the FDTised code to sys/arch/arm/nxp to match the
sys/arch/{cpu}/{vendor} convention
- FDTise some more drivers
- Secure Non-Volatile Storage
- watchdog driver
- On chip OTP
- Match fsl,imx6dl
- Add some more drivers to GENERIC that will be supported by i.MX 6
boards