Invert and rename config option

Replace MBEDTLS_PSA_COPY_CALLER_BUFFERS with inverse:
!MBEDTLS_PSA_ASSUME_EXCLUSIVE_BUFFERS. This ensures that buffer
protection is enabled by default without any change to the Mbed TLS
config file.

Signed-off-by: David Horstmann <david.horstmann@arm.com>
diff --git a/tests/src/helpers.c b/tests/src/helpers.c
index be9155c..065d17d 100644
--- a/tests/src/helpers.c
+++ b/tests/src/helpers.c
@@ -318,7 +318,7 @@
     int ret = 0;
 
 #if defined(MBEDTLS_TEST_HOOKS) && defined(MBEDTLS_PSA_CRYPTO_C) \
-    && defined(MBEDTLS_PSA_COPY_CALLER_BUFFERS) \
+    && !defined(MBEDTLS_PSA_ASSUME_EXCLUSIVE_BUFFERS) \
     && defined(MBEDTLS_TEST_MEMORY_CAN_POISON)
     mbedtls_poison_test_hooks_setup();
 #endif
@@ -348,7 +348,7 @@
 void mbedtls_test_platform_teardown(void)
 {
 #if defined(MBEDTLS_TEST_HOOKS) && defined(MBEDTLS_PSA_CRYPTO_C) \
-    && defined(MBEDTLS_PSA_COPY_CALLER_BUFFERS) \
+    && !defined(MBEDTLS_PSA_ASSUME_EXCLUSIVE_BUFFERS) \
     &&  defined(MBEDTLS_TEST_MEMORY_CAN_POISON)
     mbedtls_poison_test_hooks_teardown();
 #endif