1. There is a custom uEnv.txt file being generated by yocto build at work/build/tmp/deploy/images/zcu106-zynqmp which can be edited to set custom cma size.
2. Modify uEnv.txt bootargs option to set requried cma size as below
   • "bootargs=earlycon clk_ignore_unused root=/dev/mmcblk0p2 rw rootwait cma=1500m"
3. Copy uEnv.txt having CMA boot args setting in boot partition (i.e the first partition) of sdcard and boot the board.