Exclude MPU manager code if MPU disabled

Save around 400 bytes from images using FlashIAP by omitting MPU manager
reference counting if DEVICE_MPU is 0.

platform/mbed_mpu_mgmt.c

@@ -20,6 +20,8 @@
 #include "hal/mpu_api.h"
 #include <limits.h>
 
+#if DEVICE_MPU
+
 static uint16_t mem_xn_lock;
 static uint16_t mem_wn_lock;
 
@@ -78,3 +80,5 @@ void mbed_mpu_manager_unlock_rom_write()
     }
     core_util_critical_section_exit();
 }
+
+#endif

platform/mbed_mpu_mgmt.h

@@ -32,6 +32,8 @@
 extern "C" {
 #endif
 
+#if DEVICE_MPU
+
 /** Lock ram execute never mode off
  *
  * This disables the MPU's execute never ram protection and allows
@@ -80,6 +82,18 @@ void mbed_mpu_manager_lock_rom_write(void);
  */
 void mbed_mpu_manager_unlock_rom_write(void);
 
+#else
+
+#define mbed_mpu_manager_lock_ram_execution() (void)0
+
+#define mbed_mpu_manager_unlock_ram_execution() (void)0
+
+#define mbed_mpu_manager_lock_rom_write() (void)0
+
+#define mbed_mpu_manager_unlock_rom_write() (void)0
+
+#endif
+
 #ifdef __cplusplus
 }
 #endif