Move MBEDTLS_ERR_xxx Doxygen comments before the definition

Now that descriptions of error codes no longer have to be on the same line
for the sake of generate_errors.pl, move them to their own line before the
definition. This aligns them with what we do for other definitions, and
means that we no longer need to have very long lines containing both the C
definition and the comment.

```
perl -i -pe 's~^(#define +MBEDTLS_ERR_\w+ +-\w+) */\*[*!]<(.*)\*/~/**$2*/\n$1~' include/mbedtls/*.h
```

This commit does not change the output of generate_errors.pl.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/include/mbedtls/chacha20.h b/include/mbedtls/chacha20.h
index e59dd1f..03b4871 100644
--- a/include/mbedtls/chacha20.h
+++ b/include/mbedtls/chacha20.h
@@ -41,15 +41,18 @@
 #include <stdint.h>
 #include <stddef.h>
 
-#define MBEDTLS_ERR_CHACHA20_BAD_INPUT_DATA         -0x0051 /**< Invalid input parameter(s). */
+/** Invalid input parameter(s). */
+#define MBEDTLS_ERR_CHACHA20_BAD_INPUT_DATA         -0x0051
 
 /* MBEDTLS_ERR_CHACHA20_FEATURE_UNAVAILABLE is deprecated and should not be
  * used. */
-#define MBEDTLS_ERR_CHACHA20_FEATURE_UNAVAILABLE    -0x0053 /**< Feature not available. For example, s part of the API is not implemented. */
+/** Feature not available. For example, s part of the API is not implemented. */
+#define MBEDTLS_ERR_CHACHA20_FEATURE_UNAVAILABLE    -0x0053
 
 /* MBEDTLS_ERR_CHACHA20_HW_ACCEL_FAILED is deprecated and should not be used.
  */
-#define MBEDTLS_ERR_CHACHA20_HW_ACCEL_FAILED        -0x0055  /**< Chacha20 hardware accelerator failed. */
+/** Chacha20 hardware accelerator failed. */
+#define MBEDTLS_ERR_CHACHA20_HW_ACCEL_FAILED        -0x0055
 
 #ifdef __cplusplus
 extern "C" {