accel/tcg: Simplify tlb_plugin_lookup

Now that we defer address space update and tlb_flush until
the next async_run_on_cpu, the plugin run at the end of the
instruction no longer has to contend with a flushed tlb.
Therefore, delete SavedIOTLB entirely.

Properly return false from tlb_plugin_lookup when we do
not have a tlb match.

Fixes a bug in which SavedIOTLB had stale data, because
there were multiple i/o accesses within a single insn.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

include/hw/core/cpu.h

@@ -227,17 +227,6 @@ struct CPUWatchpoint {
     QTAILQ_ENTRY(CPUWatchpoint) entry;
 };
 
-#ifdef CONFIG_PLUGIN
-/*
- * For plugins we sometime need to save the resolved iotlb data before
- * the memory regions get moved around  by io_writex.
- */
-typedef struct SavedIOTLB {
-    MemoryRegionSection *section;
-    hwaddr mr_offset;
-} SavedIOTLB;
-#endif
-
 struct KVMState;
 struct kvm_run;
 
@@ -409,8 +398,6 @@ struct CPUState {
 
 #ifdef CONFIG_PLUGIN
     GArray *plugin_mem_cbs;
-    /* saved iotlb data from io_writex */
-    SavedIOTLB saved_iotlb;
 #endif
 
     /* TODO Move common fields from CPUArchState here. */