Move MBEDTLS_CIPHER modification to appropriate section

Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
diff --git a/configs/config-tfm.h b/configs/config-tfm.h
index 8ed0792..14896d4 100644
--- a/configs/config-tfm.h
+++ b/configs/config-tfm.h
@@ -42,11 +42,6 @@
 #undef MBEDTLS_PLATFORM_STD_EXIT_SUCCESS
 #undef MBEDTLS_PLATFORM_STD_EXIT_FAILURE
 
-/* CCM is the only cipher/AEAD enabled in TF-M configuration files, but it
- * does not need CIPHER_C to be enabled, so we can disable it in order
- * to reduce code size further. */
-#undef MBEDTLS_CIPHER_C
-
 /*
  * In order to get an example config that works cleanly out-of-the-box
  * for both baremetal and non-baremetal builds, we detect baremetal builds
@@ -66,3 +61,8 @@
 
 // We expect TF-M to pick this up soon
 #define MBEDTLS_BLOCK_CIPHER_NO_DECRYPT
+
+/* CCM is the only cipher/AEAD enabled in TF-M configuration files, but it
+ * does not need CIPHER_C to be enabled, so we can disable it in order
+ * to reduce code size further. */
+#undef MBEDTLS_CIPHER_C