The schematic of ADSP-BF518F EZ-Board shows P2 and P4 connectors are the same. Is this an error on the schematics?
There is no error in the ADSP-BF518 EZ-Kit P2 and P4 expansion interface schematics. There are many signals which are different in those connectors, please look into schematics given below.
Note that all the GPIO pins has multiplexed functionality. For instance, as you can see in the below image the pin 159 has multiplexed functionality like PH3/DT1/SPI1_MOSI_RSI_DATA7 marked inside U12 layout. The node which is connected to this pin is available on the P2 expansion interface. So it implies that you could use P2.25 as SPI1_MOSI pin. Similarly the P4.25 can be used as SPI0_MOSI.
Exerpt from ADSP-BF518 (U12) page# 92/110:
Exerpt from Expansion interface P2 page# 102/110:
Hope this clears your doubt.