Add NamedGroup IANA values and helper functions

Signed-off-by: Jerry Yu <jerry.h.yu@arm.com>
diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index f533859..725b156 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -170,6 +170,37 @@
 #define MBEDTLS_ERR_SSL_BAD_CONFIG                        -0x5E80
 
 /*
+ * TLS 1.3 NamedGroup values
+ *
+ * From RF 8446
+ *    enum {
+ *         // Elliptic Curve Groups (ECDHE)
+ *         secp256r1(0x0017), secp384r1(0x0018), secp521r1(0x0019),
+ *         x25519(0x001D), x448(0x001E),
+ *         // Finite Field Groups (DHE)
+ *         ffdhe2048(0x0100), ffdhe3072(0x0101), ffdhe4096(0x0102),
+ *         ffdhe6144(0x0103), ffdhe8192(0x0104),
+ *         // Reserved Code Points
+ *         ffdhe_private_use(0x01FC..0x01FF),
+ *         ecdhe_private_use(0xFE00..0xFEFF),
+ *         (0xFFFF)
+ *     } NamedGroup;
+ *
+ */
+/* Elliptic Curve Groups (ECDHE) */
+#define MBEDTLS_SSL_TLS13_NAMED_GROUP_SECP256R1     0x0017
+#define MBEDTLS_SSL_TLS13_NAMED_GROUP_SECP384R1     0x0018
+#define MBEDTLS_SSL_TLS13_NAMED_GROUP_SECP521R1     0x0019
+#define MBEDTLS_SSL_TLS13_NAMED_GROUP_X25519        0x001D
+#define MBEDTLS_SSL_TLS13_NAMED_GROUP_X448          0x001E
+/* Finite Field Groups (DHE) */
+#define MBEDTLS_SSL_TLS13_NAMED_GROUP_FFDHE2048     0x0100
+#define MBEDTLS_SSL_TLS13_NAMED_GROUP_FFDHE3072     0x0101
+#define MBEDTLS_SSL_TLS13_NAMED_GROUP_FFDHE4096     0x0102
+#define MBEDTLS_SSL_TLS13_NAMED_GROUP_FFDHE6144     0x0103
+#define MBEDTLS_SSL_TLS13_NAMED_GROUP_FFDHE8192     0x0104
+
+/*
  * TLS 1.3 Key Exchange Modes
  *
  * Mbed TLS internal identifiers for use with the SSL configuration API