Replace `MBEDTLS_MD_CAN_SHA512` with `PSA_WANT_ALG_SHA_512`

Signed-off-by: Gabor Mezei <gabor.mezei@arm.com>
diff --git a/library/x509.c b/library/x509.c
index 34b6a5a..06e21f2 100644
--- a/library/x509.c
+++ b/library/x509.c
@@ -149,7 +149,7 @@
         case MBEDTLS_MD_SHA384:
             return "SHA384";
 #endif
-#if defined(MBEDTLS_MD_CAN_SHA512)
+#if defined(PSA_WANT_ALG_SHA_512)
         case MBEDTLS_MD_SHA512:
             return "SHA512";
 #endif