Add mbedtls_ecc_group_to_psa() to PSA in TF-M 1.2

The PSA headers imported from TF-M does not contain a declaration of
mbedtls_ecc_group_to_psa(), which is expected by pk.c from Mbed TLS.
This leads to an "undefined symbol" error when using the ARM toolchain
to compile an application for a TF-M target.

platform/FEATURE_EXPERIMENTAL_API/FEATURE_PSA/TARGET_TFM/TARGET_TFM_LATEST/include/psa/crypto_extra.h

@@ -57,6 +57,74 @@ extern "C" {
 
 /**@}*/
 
+#if defined(MBEDTLS_ECP_C)
+#include <mbedtls/ecp.h>
+
+/** Convert an ECC curve identifier from the Mbed TLS encoding to PSA.
+ *
+ * \note This function is provided solely for the convenience of
+ *       Mbed TLS and may be removed at any time without notice.
+ *
+ * \param grpid         An Mbed TLS elliptic curve identifier
+ *                      (`MBEDTLS_ECP_DP_xxx`).
+ * \param[out] bits     On success, the bit size of the curve.
+ *
+ * \return              The corresponding PSA elliptic curve identifier
+ *                      (`PSA_ECC_FAMILY_xxx`).
+ * \return              \c 0 on failure (\p grpid is not recognized).
+ */
+static inline psa_ecc_family_t mbedtls_ecc_group_to_psa( mbedtls_ecp_group_id grpid,
+                                                        size_t *bits )
+{
+    switch( grpid )
+    {
+        case MBEDTLS_ECP_DP_SECP192R1:
+            *bits = 192;
+            return( PSA_ECC_FAMILY_SECP_R1 );
+        case MBEDTLS_ECP_DP_SECP224R1:
+            *bits = 224;
+            return( PSA_ECC_FAMILY_SECP_R1 );
+        case MBEDTLS_ECP_DP_SECP256R1:
+            *bits = 256;
+            return( PSA_ECC_FAMILY_SECP_R1 );
+        case MBEDTLS_ECP_DP_SECP384R1:
+            *bits = 384;
+            return( PSA_ECC_FAMILY_SECP_R1 );
+        case MBEDTLS_ECP_DP_SECP521R1:
+            *bits = 521;
+            return( PSA_ECC_FAMILY_SECP_R1 );
+        case MBEDTLS_ECP_DP_BP256R1:
+            *bits = 256;
+            return( PSA_ECC_FAMILY_BRAINPOOL_P_R1 );
+        case MBEDTLS_ECP_DP_BP384R1:
+            *bits = 384;
+            return( PSA_ECC_FAMILY_BRAINPOOL_P_R1 );
+        case MBEDTLS_ECP_DP_BP512R1:
+            *bits = 512;
+            return( PSA_ECC_FAMILY_BRAINPOOL_P_R1 );
+        case MBEDTLS_ECP_DP_CURVE25519:
+            *bits = 255;
+            return( PSA_ECC_FAMILY_MONTGOMERY );
+        case MBEDTLS_ECP_DP_SECP192K1:
+            *bits = 192;
+            return( PSA_ECC_FAMILY_SECP_K1 );
+        case MBEDTLS_ECP_DP_SECP224K1:
+            *bits = 224;
+            return( PSA_ECC_FAMILY_SECP_K1 );
+        case MBEDTLS_ECP_DP_SECP256K1:
+            *bits = 256;
+            return( PSA_ECC_FAMILY_SECP_K1 );
+        case MBEDTLS_ECP_DP_CURVE448:
+            *bits = 448;
+            return( PSA_ECC_FAMILY_MONTGOMERY );
+        default:
+            *bits = 0;
+            return( 0 );
+    }
+}
+
+#endif /* MBEDTLS_ECP_C */
+
 #ifdef __cplusplus
 }
 #endif