Extract MPI_CORE(add) from the prototype

Signed-off-by: Tom Cosgrove <tom.cosgrove@arm.com>

library/bignum_core.h

@@ -277,6 +277,29 @@ int mbedtls_mpi_core_write_be( const mbedtls_mpi_uint *A,
 void mbedtls_mpi_core_shift_r( mbedtls_mpi_uint *X, size_t limbs,
                                size_t count );
 
+#define MPI_CORE(func) mbedtls_mpi_core_ ## func ## _minimal
+
+/**
+ * \brief Add two known-size large unsigned integers, returning the carry.
+ *
+ * Calculate l + r where l and r have the same size.
+ * This function operates modulo (2^ciL)^n and returns the carry
+ * (1 if there was a wraparound, and 0 otherwise).
+ *
+ * d may be aliased to l or r.
+ *
+ * \param[out] d        The result of the addition.
+ * \param[in] l         The left operand.
+ * \param[in] r         The right operand.
+ * \param n             Number of limbs of \p d, \p l and \p r.
+ *
+ * \return              1 if `l + r >= (2^{ciL})^n`, 0 otherwise.
+ */
+mbedtls_mpi_uint MPI_CORE(add)( mbedtls_mpi_uint *d,
+                                const mbedtls_mpi_uint *l,
+                                const mbedtls_mpi_uint *r,
+                                size_t n );
+
 /**
  * \brief Conditional addition of two fixed-size large unsigned integers,
  *        returning the carry.