toradex: imx6: Move g_dnl_bind_fixup() into common SPL code

Instead of having every board file to add its own g_dnl_bind_fixup()
implementation, move it to the common imx6 SPL code.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Reviewed-by: Łukasz Majewski <lukma@denx.de>