tools: imx8mimage: Keep IVT reserved1 field zero always

tools: imx8mimage: Keep IVT reserved1 field zero always

Since 1931a35cb55 ("imx: HAB: Validate IVT before authenticating image")
the U-Boot HAB implementation is checking whether reserved1 field in IVT
is zero or not. In case the field is not zero, IVT validation fails. Stop
setting IVT reserved1 field to non-zero in mkimage imx8m plugin, otherwise
the validation cannot ever work.

Note that this only affects legacy boards which do not use binman.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Fabio Estevam <festevam@denx.de>
Cc: Peng Fan <peng.fan@nxp.com>
Cc: Stefano Babic <sbabic@denx.de>