Atmega328p output voltage
Atmega328p doesn't have any output voltage, it only has input voltage, VCC and AVCC must be the same, AVCC should be connected to VCC via LC filter.

The easiest way how to connect the Nokia 5110 display is to power both uC and display from 3.3V

You said you use Arduino as ISP, make sure you use 3.3V arduino as well for this, or get a ICSP level shifter