Default.xml: meta-seco-imx: Update revision to add support for mainline U-Boot's binman tools - issue 462

MR for #462 (closed).

Commit made to meta-seco-imx: https://git.seco.com/pub/i.mx/yocto/5.x/meta-seco-imx/-/commit/8898fd983ce80ada8466619016c99fd8bb24e8f9

These changes will not yet affect the actual build for seco-imx8mm-c61-2g/4g machines, because the machine overrides, which triggers mainline U-Boot build, is commented out. It is just an intermediate issue MR.