Honor Memory mapped devices as hint for the decompiler

[radare]

Related info: https://twitter.com/rfc6919/status/1103793517346738176?s=21

<pancake> if a io map is named mmd.* something 
<pancake> then consider it from the decompiler that this is a memory mapped region

there's no way in r2 to specify that a region is memory mapped, but we can use this naming convention to do that. at the end in r2 we only care about this with rebased flags and esil scripts to emulate hardware... so we dont really need any special change in the io layer to handle this