exec.c: Add cpu_get_address_space()

Add a function to return the AddressSpace for a CPU based on
its numerical index. (Callers outside exec.c don't have access
to the CPUAddressSpace struct so can't just fish it out of the
CPUState struct directly.)

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Acked-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>

exec.c

@@ -564,6 +564,12 @@ void cpu_address_space_init(CPUState *cpu, AddressSpace *as, int asidx)
         memory_listener_register(&newas->tcg_as_listener, as);
     }
 }
+
+AddressSpace *cpu_get_address_space(CPUState *cpu, int asidx)
+{
+    /* Return the AddressSpace corresponding to the specified index */
+    return cpu->cpu_ases[asidx].as;
+}
 #endif
 
 #ifndef CONFIG_USER_ONLY