2 is the number of SPI interfaces so the Spec says.
Yes, you are quite right: It depends on the chip. There are two distinct ways an SPI interface can be set up in a PSoC: Using an SCB (Serial Control Block) or an UDB (Universal Digital Block). In Creator at the very right hand side of the window is a "Resource Meter" that shows how many resources your selected chip has got and (after a successful built) how many of the resources are used/free.
When in need of SPI interfaces you may consider gating/multiplexing the signals (clock) to increase the number of slaves connected.