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:
Here is a document on how to generated the SDK package:
Hope it helps!
Technical Support Engineer