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_pem.function b/tests/suites/test_suite_pem.function
index f4ac368..6328247 100644
--- a/tests/suites/test_suite_pem.function
+++ b/tests/suites/test_suite_pem.function
@@ -3,7 +3,7 @@
 #include "mbedtls/pem.h"
 #include "mbedtls/des.h"
 #include "mbedtls/aes.h"
-#include "legacy_or_psa.h"
+#include "mbedtls/legacy_or_psa.h"
 
 /* END_HEADER */