That AT86RF215 shows operating range DEVDD/EVDD digital and analog external supply voltages of 1.8 to 3.6V, table 10.1.
For the MFPS095T, GPIO aux Vdd looks the most stringent, between 3.135 and 3.465V, table 3-2.
Why wouldn't a standard 3.3V for both devices work?
The way I dealt with exactly this mismatch in one of my designs was to use a 3.15V regulator, TPS799315 in my case. which was chosen for its low noise and high PSRR in my mixed signal application, as one device was 3.0 to 3.6V and the other maxed out at 3.3V, so I picked the happy medium.