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>