Why does the CC112x chip need a 40MHz oscillator and the 32kHz auto-calibrated RC oscillator

Not sure what you mean.

CC1120 only runs on a 32 MHz clock, CC1125 runs on either 32 MHz or 40 MHz. The RC osc frequency will be dependent on the xtal frequency since the calibration uses this as a reference.

Thank you for the speedy reply. Am I correct in saying the external crystal on the XOSC_Q1 and XOSC_Q2 pins (or a TCXO on pin 32) are what provides these clocks?

Yes. The RCOSC is calibrated against the reference clock which is either a xtal or a TCXO