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/pem.h b/include/mbedtls/pem.h
index 4769bec..dfb4ff2 100644
--- a/include/mbedtls/pem.h
+++ b/include/mbedtls/pem.h
@@ -36,15 +36,24 @@
  * PEM data.
  * \{
  */
-#define MBEDTLS_ERR_PEM_NO_HEADER_FOOTER_PRESENT          -0x1080  /**< No PEM header or footer found. */
-#define MBEDTLS_ERR_PEM_INVALID_DATA                      -0x1100  /**< PEM string is not as expected. */
-#define MBEDTLS_ERR_PEM_ALLOC_FAILED                      -0x1180  /**< Failed to allocate memory. */
-#define MBEDTLS_ERR_PEM_INVALID_ENC_IV                    -0x1200  /**< RSA IV is not in hex-format. */
-#define MBEDTLS_ERR_PEM_UNKNOWN_ENC_ALG                   -0x1280  /**< Unsupported key encryption algorithm. */
-#define MBEDTLS_ERR_PEM_PASSWORD_REQUIRED                 -0x1300  /**< Private key password can't be empty. */
-#define MBEDTLS_ERR_PEM_PASSWORD_MISMATCH                 -0x1380  /**< Given private key password does not allow for correct decryption. */
-#define MBEDTLS_ERR_PEM_FEATURE_UNAVAILABLE               -0x1400  /**< Unavailable feature, e.g. hashing/encryption combination. */
-#define MBEDTLS_ERR_PEM_BAD_INPUT_DATA                    -0x1480  /**< Bad input parameters to function. */
+/** No PEM header or footer found. */
+#define MBEDTLS_ERR_PEM_NO_HEADER_FOOTER_PRESENT          -0x1080
+/** PEM string is not as expected. */
+#define MBEDTLS_ERR_PEM_INVALID_DATA                      -0x1100
+/** Failed to allocate memory. */
+#define MBEDTLS_ERR_PEM_ALLOC_FAILED                      -0x1180
+/** RSA IV is not in hex-format. */
+#define MBEDTLS_ERR_PEM_INVALID_ENC_IV                    -0x1200
+/** Unsupported key encryption algorithm. */
+#define MBEDTLS_ERR_PEM_UNKNOWN_ENC_ALG                   -0x1280
+/** Private key password can't be empty. */
+#define MBEDTLS_ERR_PEM_PASSWORD_REQUIRED                 -0x1300
+/** Given private key password does not allow for correct decryption. */
+#define MBEDTLS_ERR_PEM_PASSWORD_MISMATCH                 -0x1380
+/** Unavailable feature, e.g. hashing/encryption combination. */
+#define MBEDTLS_ERR_PEM_FEATURE_UNAVAILABLE               -0x1400
+/** Bad input parameters to function. */
+#define MBEDTLS_ERR_PEM_BAD_INPUT_DATA                    -0x1480
 /* \} name */
 
 #ifdef __cplusplus