imx: makefile: drop the use of imx8mimage.sh

After switch to use binman, no need to use the bash script
to check file exsiting or not. And there is bug that
the script will be executed everytime Makefile is used which is
confusing people.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Tested-by: Frieder Schrempf <frieder.schrempf@kontron.de>
1 file changed