Changed every memcmp to SCA equivalent mbedtls_platform_memcmp

This makes physical attacks more difficult.
Selftest memcmp functions were not changed.
diff --git a/library/rsa.c b/library/rsa.c
index 3bfc73e..e3d5124 100644
--- a/library/rsa.c
+++ b/library/rsa.c
@@ -2266,7 +2266,7 @@
     if ( ret != 0 )
         goto exit;
 
-    if( memcmp( hash_start, result, hlen ) != 0 )
+    if( mbedtls_platform_memcmp( hash_start, result, hlen ) != 0 )
     {
         ret = MBEDTLS_ERR_RSA_VERIFY_FAILED;
         goto exit;