System_Defs.h does not handle all parts for SPI definitions

[lstandage]

A customer on the Digilent forums observed that just adding the DSPI library for the chipKIT Pro MX4 does not compile due to missing definitions for these macros:
_SPI2_IPL_ISR
_SPI2_IPL_IPC
_SPI2_SPL_IPC

Looking at System_Defs.h, it looks like the SPI2 definitions will not be handled for the 3xx/4xx parts.

The first case handled is for PPS devices.
Second case is for 5xx/6xx/7xx devices

And that's it.

So the resolution will be to add 3xx/4xx non-PPS definition.