exec.c: Handle IOMMUs in address_space_translate_for_iotlb()

Currently we don't support board configurations that put an IOMMU
in the path of the CPU's memory transactions, and instead just
assert() if the memory region fonud in address_space_translate_for_iotlb()
is an IOMMUMemoryRegion.

Remove this limitation by having the function handle IOMMUs.
This is mostly straightforward, but we must make sure we have
a notifier registered for every IOMMU that a transaction has
passed through, so that we can flush the TLB appropriately
when any of the IOMMUs change their mappings.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-id: 20180604152941.20374-5-peter.maydell@linaro.org

include/exec/exec-all.h

@@ -478,7 +478,8 @@ void tb_flush_jmp_cache(CPUState *cpu, target_ulong addr);
 
 MemoryRegionSection *
 address_space_translate_for_iotlb(CPUState *cpu, int asidx, hwaddr addr,
-                                  hwaddr *xlat, hwaddr *plen);
+                                  hwaddr *xlat, hwaddr *plen,
+                                  MemTxAttrs attrs, int *prot);
 hwaddr memory_region_section_get_iotlb(CPUState *cpu,
                                        MemoryRegionSection *section,
                                        target_ulong vaddr,