AST2520A2-GP is a ASPEED Technology processing device.
This device provides the compute or control function for the system, with its interfaces and memory documented by the manufacturer.
This ordering code is specified at 456.
It is used in embedded control and signal processing, where the part has to keep its specification over the life of the equipment.
What differs here is Function Integrated remote management processor, together with CPU Arm1176JZS, up to 800 MHz.
Its Memory Interface is stated as 16-bit DDR3L/DDR4 in the data sheet.
The reason to choose it is the fit between the specification and the function it performs on the board.