I have no idea about this interface, If I want a cortex-M processor work with a cortex-A or R processor in a small system, will this port provide a fast path between these two processors?
The Co-processor interface is used to extend the processor functionality.
I don't believe it could be used as some sort of interface between processors.
Note that not all Cortex-M processors support the interface:
https://developer.arm.com/documentation/ka001165
Thank you Ronan, but I don't find any IPs that can be connected to this port in ARM IP products, does that means I need to design my own IP to extend the processor?
Yes, correct.
Co-processor designs used to be more common to accelerate specific operations. System design advancements make these less valuable nowadays. They are often implemented simply as memory mapped peripherals.