Make legacy_or_psa.h public.

As a public header, it should no longer include common.h, just use
build_info.h which is what we actually need anyway.

Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
diff --git a/tests/suites/test_suite_x509write.function b/tests/suites/test_suite_x509write.function
index 5a97240..1120bee 100644
--- a/tests/suites/test_suite_x509write.function
+++ b/tests/suites/test_suite_x509write.function
@@ -7,7 +7,7 @@
 #include "mbedtls/rsa.h"
 
 #include "hash_info.h"
-#include "legacy_or_psa.h"
+#include "mbedtls/legacy_or_psa.h"
 
 #if defined(MBEDTLS_RSA_C)
 int mbedtls_rsa_decrypt_func( void *ctx, size_t *olen,