Revert "Remove deprecated things from hashing modules"

This reverts commit c75d9f589bf392177dbeba7704693e53fe55cb19.

This was merged by mistake in development instead of development_3.0.

Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
diff --git a/include/mbedtls/md.h b/include/mbedtls/md.h
index 2d08195..e4354ba 100644
--- a/include/mbedtls/md.h
+++ b/include/mbedtls/md.h
@@ -38,8 +38,6 @@
 #define MBEDTLS_ERR_MD_ALLOC_FAILED                       -0x5180  /**< Failed to allocate memory. */
 #define MBEDTLS_ERR_MD_FILE_IO_ERROR                      -0x5200  /**< Opening or reading of file failed. */
 
-// TODO [TR] for #4029: can't remove it because it's still used in the code.
-// see the other TODOs
 /* MBEDTLS_ERR_MD_HW_ACCEL_FAILED is deprecated and should not be used. */
 #define MBEDTLS_ERR_MD_HW_ACCEL_FAILED                    -0x5280  /**< MD hardware accelerator failed. */
 
@@ -160,6 +158,33 @@
  */
 void mbedtls_md_free( mbedtls_md_context_t *ctx );
 
+#if ! defined(MBEDTLS_DEPRECATED_REMOVED)
+#if defined(MBEDTLS_DEPRECATED_WARNING)
+#define MBEDTLS_DEPRECATED    __attribute__((deprecated))
+#else
+#define MBEDTLS_DEPRECATED
+#endif
+/**
+ * \brief           This function selects the message digest algorithm to use,
+ *                  and allocates internal structures.
+ *
+ *                  It should be called after mbedtls_md_init() or mbedtls_md_free().
+ *                  Makes it necessary to call mbedtls_md_free() later.
+ *
+ * \deprecated      Superseded by mbedtls_md_setup() in 2.0.0
+ *
+ * \param ctx       The context to set up.
+ * \param md_info   The information structure of the message-digest algorithm
+ *                  to use.
+ *
+ * \return          \c 0 on success.
+ * \return          #MBEDTLS_ERR_MD_BAD_INPUT_DATA on parameter-verification
+ *                  failure.
+ * \return          #MBEDTLS_ERR_MD_ALLOC_FAILED on memory-allocation failure.
+ */
+int mbedtls_md_init_ctx( mbedtls_md_context_t *ctx, const mbedtls_md_info_t *md_info ) MBEDTLS_DEPRECATED;
+#undef MBEDTLS_DEPRECATED
+#endif /* MBEDTLS_DEPRECATED_REMOVED */
 
 /**
  * \brief           This function selects the message digest algorithm to use,