target/microblaze: Cache mem_index in DisasContext

Ideally, nothing outside the top-level of translation even
has access to env.  Cache the value in init_disas_context.

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>
1 file changed