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/library/x509.c b/library/x509.c
index aa39517..f1d988a 100644
--- a/library/x509.c
+++ b/library/x509.c
@@ -62,7 +62,7 @@
 #include <time.h>
 #endif
 
-#include "legacy_or_psa.h"
+#include "mbedtls/legacy_or_psa.h"
 
 #define CHECK(code) if( ( ret = ( code ) ) != 0 ){ return( ret ); }
 #define CHECK_RANGE(min, max, val)                      \