Add a MemTxAttrs field to the IOTLB, and allow target-specific
code to set it via a new tlb_set_page_with_attrs() function;
pass the attributes through to the device when making IO accesses.
Backports commit fadc1cbe85c6b032d5842ec0d19d209f50fcb375 from qemu
Make the CPU iotlb a structure rather than a plain hwaddr;
this will allow us to add transaction attributes to it.
Backports commit e469b22ffda40188954fafaf6e3308f58d50f8f8 from qemu