Move the PSA_ASSERT macro to the common helpers file

It's potentially useful in all PSA test suites, of which there are now
several.

tests/suites/helpers.function

@@ -90,6 +90,14 @@ typedef struct data_tag
         }                                           \
     } while( 0 )
 
+/** Evaluate an expression and fail the test case if it returns an error.
+ *
+ * \param expr      The expression to evaluate. This is typically a call
+ *                  to a \c psa_xxx function that returns a value of type
+ *                  #psa_status_t.
+ */
+#define PSA_ASSERT( expr ) TEST_ASSERT( ( expr ) == PSA_SUCCESS )
+
 /** Allocate memory dynamically and fail the test case if this fails.
  *
  * You must set \p pointer to \c NULL before calling this macro and

tests/suites/test_suite_psa_crypto_slot_management.function

@@ -8,8 +8,6 @@
 
 #include "psa_crypto_storage.h"
 
-#define PSA_ASSERT( expr ) TEST_ASSERT( ( expr ) == PSA_SUCCESS )
-
 typedef enum
 {
     CLOSE_BY_CLOSE,