User-space programs cannot use the 64-bit lwea/swea instructions.
We can improve code generation and runtime by restricting the
user-only address space to 32-bit.

Tested-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>