Add error code MBEDTLS_ERR_PLATFORM_FAULT_DETECTED

This can be used by Mbed TLS functions in any module to signal that a fault
attack is likely happening, so this can be appropriately handled by the
application (report, fall back to safer mode or even halt, etc.)
diff --git a/include/mbedtls/error.h b/include/mbedtls/error.h
index 31f294f..a52f9f5 100644
--- a/include/mbedtls/error.h
+++ b/include/mbedtls/error.h
@@ -86,7 +86,7 @@
  * CHACHA20  3                  0x0051-0x0055
  * POLY1305  3                  0x0057-0x005B
  * CHACHAPOLY 2 0x0054-0x0056
- * PLATFORM  1  0x0070-0x0072
+ * PLATFORM  3  0x0070-0x0072   0x0071-0x0071
  *
  * High-level module nr (3 bits - 0x0...-0x7...)
  * Name      ID  Nr of Errors