Modifications and development of the P2020DS Linux u-boot and kernel code is done in the P2020DS BSP, or ltib, not in CodeWarrior Dev Studio. Go to http://www.freescale.com/powerbsp, download the package for the P2020DS to your Linux machine and install it there. Documentation is included but if you're new to using an ltib then I recommend researching your questions on-line. www.google.com/linux is a good starting point.
The Eclipse-based CodeWarrior Dev Studio for QorIQ is still in development but is scheduled for release this Summer. Watch the announcements on www.freescale.com for details. I hope this helps.