Deepti - You can find lwip 2.0.0 support in our platforms that were released with release 5 (this is a subset of the overall supported SoCs). If your platform was not in the release 5 release, you can expect lwip 2.0.0 for your platform in release 6, coming in March 2017.
I am working with FRDMK64F board and have been using SDK_2.0_FRDM-K64F past few months. From nxp website, today I downloaded the latest SDK for my board: SDK_2.1_FRDM-K64F. But I am not clear what you mean by release 5. I could not find it.
Also, in the SDK2.1, I did find that lwip 2.0.0 was supported but its not the lwip 2.0.0-final release(released on 10 nov-2016). It is lwip 2.0.0 RC0. When you say lwip 2.0.0 is supported in release 5 and the release 6 coming in March 2017, do you mean lwip 2.0.0-RC0 or lwip 2.0.0-final release?