what kind of Processors and GPU are used for Aircraft display ? Is it possible to use single processor to run all three displays (Primary flight display, Navigation display and EICAS)?
Airplanes have a long history of evolution, and so do computers.
But some latest developments seems to suggest that, yes, people are working on it to use a single computer system to display and control everything, but right now the innovation front is in the automotive industry where regulatory complexity is lower.
Rockwell Collins Pro Line Fusion, the current state of the art, adopted the Radeon E2400 in 2012 to drive the displays (that's pretty new by aviation standards).
There is no way that a single processor would be used to drive multiple displays as that kind of single-point-of-failure possibility for that level of criticality is simply not allowed.
The older cathode ray tube stuff will use processors from the 80s, like the 286.