FIFO Memory Volatile or Non Volatile
While the datasheet may not state that these FIFOs are volatile, their normal use would require a volatile memory, as they will normally be written to frequently, at full processor speeds, like normal RAM. 

Non-volatile solid state memory (EEPROM, FLASH) can usually only tolerate a limited number of write cycles, and usually requires special slow operations for writes, so would not be suitable for use in a FIFO.