target/microblaze: Split out MSR from env->sregs

Continue eliminating the sregs array in favor of individual members.
Does not correct the width of MSR, yet.

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>
6 files changed