Add SCR file SCR-imx-lib.txt for imx-mkimage

This patch add SCR file SCR-imx-mkimage.txt, btw, this patch also rename file
COPYING to LICENSE according to the suggestion of Ann Thornton.

Suggested-by: Ann Thornton <ann.thornton@nxp.com>
Reviewed-by: Ann Thornton <ann.thornton@nxp.com>
Signed-off-by: Jason Liu <jason.hui.liu@nxp.com>