When we added the _with_attrs accessors we forgot to mention
them in the documentation.
Backports commit 687ac05d71bbb3172e0546248e40483ef43a4813 from qemu
Now that all the users of old_mmio MemoryRegion accessors
have been converted, we can remove the core code support.
Backports commit 62a0db942dec6ebfec19aac2b604737d3c9a2d75 from qemu