[External Peripherals] Define external peripheral read/write to Ripes memory

[mortbopet]

For peripherals such as DMAs, a peripheral may need to access the internal simulator memory. This is currently supported by the following functions, which may be set by a peripheral:

https://github.com/mortbopet/Ripes/blob/daad80f7de5c82a8662ecefb02150770619fc311/src/io/iobase.h#L116-L120

A protocol needs to be implemented to handle memory accesses from the peripheral server to the Ripes memory.