firmware: imx: Move i.MX SCU soc driver into imx firmware folder

The i.MX SCU soc driver depends on SCU firmware driver, so it has to
use platform driver model for proper defer probe operation, since
it has no device binding in DT file, a simple platform device is
created together inside the platform driver. To make it more clean,
we can just move the entire SCU soc driver into imx firmware folder
and initialized by i.MX SCU firmware driver.

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>