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/pkcs12.h b/include/mbedtls/pkcs12.h
index 4b8ce7e..ba9180b 100644
--- a/include/mbedtls/pkcs12.h
+++ b/include/mbedtls/pkcs12.h
@@ -34,10 +34,14 @@
 
 #include <stddef.h>
 
-#define MBEDTLS_ERR_PKCS12_BAD_INPUT_DATA                 -0x1F80  /**< Bad input parameters to function. */
-#define MBEDTLS_ERR_PKCS12_FEATURE_UNAVAILABLE            -0x1F00  /**< Feature not available, e.g. unsupported encryption scheme. */
-#define MBEDTLS_ERR_PKCS12_PBE_INVALID_FORMAT             -0x1E80  /**< PBE ASN.1 data not as expected. */
-#define MBEDTLS_ERR_PKCS12_PASSWORD_MISMATCH              -0x1E00  /**< Given private key password does not allow for correct decryption. */
+/** Bad input parameters to function. */
+#define MBEDTLS_ERR_PKCS12_BAD_INPUT_DATA                 -0x1F80
+/** Feature not available, e.g. unsupported encryption scheme. */
+#define MBEDTLS_ERR_PKCS12_FEATURE_UNAVAILABLE            -0x1F00
+/** PBE ASN.1 data not as expected. */
+#define MBEDTLS_ERR_PKCS12_PBE_INVALID_FORMAT             -0x1E80
+/** Given private key password does not allow for correct decryption. */
+#define MBEDTLS_ERR_PKCS12_PASSWORD_MISMATCH              -0x1E00
 
 #define MBEDTLS_PKCS12_DERIVE_KEY       1   /**< encryption/decryption key */
 #define MBEDTLS_PKCS12_DERIVE_IV        2   /**< initialization vector     */