target-microblaze: Convert use-mmu to a CPU property

Originally the use-mmu PVR bits were manually set for each machine. This
is a hassle and difficult to read, instead set them based on the CPU
properties.

Signed-off-by: Alistair Francis <alistair.francis@xilinx.com>
Reviewed-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Signed-off-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>

target-microblaze/cpu-qom.h

@@ -64,6 +64,7 @@ typedef struct MicroBlazeCPU {
         bool stackprot;
         uint32_t base_vectors;
         uint8_t use_fpu;
+        bool use_mmu;
     } cfg;
 
     CPUMBState env;