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/src/certs.c b/tests/src/certs.c
index 5516026..ca03b29 100644
--- a/tests/src/certs.c
+++ b/tests/src/certs.c
@@ -23,7 +23,7 @@
 
 #include "mbedtls/build_info.h"
 
-#include "legacy_or_psa.h"
+#include "mbedtls/legacy_or_psa.h"
 
 /*
  * Test CA Certificates