exec: split out non-softmmu-specific parts

Over the years, most parts of exec.c that were not specific to softmmu
have been moved to accel/tcg; what's left is mostly the low-level part
of the memory API, which includes RAMBlock and AddressSpaceDispatch.
However exec.c also hosts 4-500 lines of code for the target specific
parts of the CPU QOM object, plus a few functions for user-mode
emulation that do not have a better place (they are not TCG-specific so
accel/tcg/user-exec.c is not a good place either).

Move these parts to a new file, so that exec.c can be moved to
softmmu/physmem.c.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

include/exec/cpu-common.h

@@ -14,6 +14,9 @@ void cpu_list_unlock(void);
 
 void tcg_flush_softmmu_tlb(CPUState *cs);
 
+void tcg_iommu_init_notifier_list(CPUState *cpu);
+void tcg_iommu_free_notifier_list(CPUState *cpu);
+
 #if !defined(CONFIG_USER_ONLY)
 
 enum device_endian {