The SPI NOR minimum subsector size is 4 kiB, update the alignment.
THis is particularly important in case of embedded DUMMY_DDR, which
must be at at least 4 kiB aligned offset.
Fixes: a2b96ece5be1 ("tools: add i.MX8/8X image support") Signed-off-by: Marek Vasut <marex@nabladev.com> Reviewed-by: Peng Fan <peng.fan@nxp.com>