Rework MPU layout for future changes

Create a dedicated MPU directory for standard Arm MPU implementations
in preparation for the Arm v8m MPU. Replace MBED_MPU_ENABLED with
DEVICE_MPU to align with the porting layer of other HAL APIs.

TESTS/mbed_hal/mpu/main.cpp

@@ -23,8 +23,7 @@
 
 #include "mpu_api.h"
 
-// Define included by mpu_api.h
+#if !DEVICE_MPU
-#if !MBED_MPU_ENABLED
 #error [NOT_SUPPORTED] MPU API not supported for this target
 #endif
 

hal/mpu/mbed_mpu_v7m.c

@@ -16,6 +16,13 @@
 #include "hal/mpu_api.h"
 #include "cmsis.h"
 
+#if ((__ARM_ARCH_7M__ == 1U) || (__ARM_ARCH_7EM__ == 1U) || (__ARM_ARCH_6M__ == 1U)) && \
+    defined (__MPU_PRESENT) && (__MPU_PRESENT == 1U)
+
+#if !DEVICE_MPU
+#error "Device has v7m MPU but it is not enabled. Add 'MPU' to device_has in targets.json"
+#endif
+
 void mbed_mpu_init()
 {
     mbed_mpu_enable_ram_xn(false);
@@ -28,7 +35,6 @@ void mbed_mpu_free()
 
 void mbed_mpu_enable_ram_xn(bool enable)
 {
-#if MBED_MPU_ENABLED
     // Flush memory writes before configuring the MPU.
     __DSB();
 
@@ -145,5 +151,6 @@ void mbed_mpu_enable_ram_xn(bool enable)
     // Ensure changes take effect
     __ISB();
     __DSB();
-#endif
 }
+
+#endif

hal/mpu_api.h

@@ -19,33 +19,15 @@
 #ifndef MBED_MPU_API_H
 #define MBED_MPU_API_H
 
+#include "device.h"
 #include <stdbool.h>
-#include "cmsis.h"
-
-#ifndef MBED_MPU_ENABLED
-
-#if ((__ARM_ARCH_7M__     == 1U) || \
-    (__ARM_ARCH_7EM__     == 1U) || \
-    (__ARM_ARCH_6M__ == 1U))
-#if defined (__MPU_PRESENT) && (__MPU_PRESENT == 1U)
-#define MBED_MPU_ENABLED      1U
-#else
-#define MBED_MPU_ENABLED      0U
-#endif
-#elif ((__ARM_ARCH_7A__ == 1U) || \
-      (__ARM_ARCH_8M_BASE__ == 1U) || \
-      (__ARM_ARCH_8M_MAIN__ == 1U))
-#define MBED_MPU_ENABLED      0U
-#else
-#error "Unknown architecture for MPU"
-#endif
-
-#endif
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
+#if DEVICE_MPU
+
 /**
  * Initialize the MPU
  *
@@ -71,6 +53,16 @@ void mbed_mpu_enable_ram_xn(bool enable);
  */
 void mbed_mpu_free(void);
 
+#else
+
+#define mbed_mpu_init()
+
+#define mbed_mpu_enable_ram_xn(enable) (void)enable
+
+#define mbed_mpu_free()
+
+#endif
+
 #ifdef __cplusplus
 }
 #endif