Hi Subodh Mankar,
Which example projects are you using? The LPC5460x_SPIFI_GENERIC.cfx file is the Flash driver file, it is located in the following folder inside the MCUXpresso IDE installation:
I would recommend you to check the MCUXpresso SDK examples, you can download the package for the LPC54608 MCUs from this link:
Welcome to MCUXpresso | MCUXpresso Config Tools
Here is a document on how to generated the SDK package:
https://community.nxp.com/docs/DOC-333304
Hope it helps!
Best Regards,
Carlos Mendoza
Technical Support Engineer