I have read that EZUSB cannot attain 115200 baudrate without using an external oscillator.
Is that also true for FX2LP ?
Yep. The timer part of it same in both.
This mainly has to do with the accuracy of the clock source required. Hence the clock requirement.
Had a look at the TRM again. FX2LP implements a separate register UART230 which helps in achieving the standard 115.2k and 230.4k without the use of external oscillator.