exec.c: Allow target CPUs to define multiple AddressSpaces

Allow multiple calls to cpu_address_space_init(); each
call adds an entry to the cpu->ases array at the specified
index. It is up to the target-specific CPU code to actually use
these extra address spaces.

Since this multiple AddressSpace support won't work with
KVM, add an assertion to avoid confusing failures.

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

include/exec/exec-all.h

@@ -96,6 +96,10 @@ void cpu_reloading_memory_map(void);
  * The target-specific code which registers ASes is responsible
  * for defining what semantics address space 0, 1, 2, etc have.
  *
+ * Before the first call to this function, the caller must set
+ * cpu->num_ases to the total number of address spaces it needs
+ * to support.
+ *
  * Note that with KVM only one address space is supported.
  */
 void cpu_address_space_init(CPUState *cpu, AddressSpace *as, int asidx);