target/microblaze: Fix width of ESR

The exception status register is only 32-bits wide.
Do not use a 64-bit type to represent it.

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>
5 files changed