arm64: add mpu_usedregion interface

Add mpu_usedregion() function to query the number of MPU regions currently in use.
This interface complements existing mpu_allocregion() and mpu_freeregion() functions,
allowing callers to determine the occupancy of the MPU region pool.

Signed-off-by: hujun5 <hujun5@xiaomi.com>

arch/arm64/src/common/arm64_mpu.c

@@ -162,6 +162,34 @@ unsigned int mpu_allocregion(void)
   return i;
 }
 
+/****************************************************************************
+ * Name: mpu_allocregion
+ *
+ * Description:
+ *   Get the number of MPU region used
+ *
+ * Input Parameters:
+ *   None
+ *
+ * Returned Value:
+ *   The the number of MPU region used
+ *
+ ****************************************************************************/
+
+unsigned int mpu_usedregion(void)
+{
+  unsigned int n = g_mpu_region[this_cpu()];
+  unsigned int count = 0;
+
+  while (n)
+    {
+      count += n & 1;
+      n >>= 1;
+    }
+
+  return count;
+}
+
 /****************************************************************************
  * Name: mpu_freeregion
  *

arch/arm64/src/common/arm64_mpu.h

@@ -383,6 +383,22 @@ unsigned int mpu_allocregion(void);
 
 void mpu_freeregion(unsigned int region);
 
+/****************************************************************************
+ * Name: mpu_allocregion
+ *
+ * Description:
+ *   Get the number of MPU region used
+ *
+ * Input Parameters:
+ *   None
+ *
+ * Returned Value:
+ *   The the number of MPU region used
+ *
+ ****************************************************************************/
+
+unsigned int mpu_usedregion(void);
+
 /****************************************************************************
  * Name: arm64_mpu_enable
  *