xilinx: Increase max size of image from 60 to 100MB

Recently big Linux kernels can have more then 60MB that's why increase this
limit to also cover these large kernels.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Link: https://lore.kernel.org/r/f52f7c8ea419d69b248ba1460a96d1635194e128.1648551279.git.michal.simek@xilinx.com