The MPC5777C reset system (ref manual chapter 50) includes a voltage sensing system to hold it in reset until the supplies become valid. So, is it safe to assume that we do not have to provide any external power-on reset to it? We understand that if we want to reset it, we could drive the pin, but we don't want to provide a redundant input ....
It is not necessary to keep /RESET pin asserted during POR how it was with MPC55xx family due to functional point of view. But do not have /RESET pin connected is little bit uncommon practice because usually it must be a way to reset the system for whatever reason (mostly several reasons - user button, debugger, external SBC chip or watchdog, or other surrounding circuits).
Another point is that if power supply is out of range, MPC5777C shall be kept in reset or unpowered. For instance, if you see notes below Absolute maximum ratings for 5V:
“Allowed 5.5 V – 6.0 V for 60 seconds cumulative time with no restrictions, for 10 hours cumulative time device in reset, TJ= 150 °C; remaining time at or below 5.5 V”
Thus, it is safer and recommended to use external power supply management circuits as it is common for most of applications.