I hope this link is useful for you Booting i.MX6 under one second - i.MXDev Blog
Remove the uboot bootloader and use whoosh simple booter for imx6:
GitHub - alexandrebelloni/whoosh: fast bootloader for ARM platforms
For the kernel remove any option that is not used in your application, the smaller the better. Also when dealing with the RFS not all the systems have the same mount time.
More info:
Boot an i.MX6 in 0.58 seconds - Boundary Devices
http://www.elinux.org/images/d/d1/Alexandre_Belloni_boottime_optimizations.pdf
for linux fast boot, you can refer to the document as below:
Linux Fast Boot on i.MX6Q Board: Building Steps
Linux Fast Boot on i.MX6 Sabresd Board
and I send the link to describe what the fast boot really is.
on clicking the above fast boot-Android Wiki link , my antvirus showed threat!