target/microblaze: Move mmu parameters to MicroBlazeCPUConfig

The final 4 fields in MicroBlazeMMU are configuration constants.
Move them into MicroBlazeCPUConfig where they belong.

Remove the leading "c_" from the member names, as that presumably
implied "config", and that should not be explicit in the location.

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>