uboot-imx

tools: zynqmpimage: Align image_size/image_stored_size

Bootrom is not capable to work with non aligned bootloader sizes.
SPL with OF_SEPARATE generates non-align images quite often that's
why this change is required before OF_SEPARATE enableding.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>