Error codes for hardware accelerator failures

Add MBEDTLS_ERR_XXX_HW_ACCEL_FAILED error codes for all cryptography
modules where the software implementation can be replaced by a hardware
implementation.

This does not include the individual message digest modules since they
currently have no way to return error codes.

This does include the higher-level md, cipher and pk modules since
alternative implementations and even algorithms can be plugged in at
runtime.
diff --git a/include/mbedtls/blowfish.h b/include/mbedtls/blowfish.h
index 6593730..c0ef5a0 100644
--- a/include/mbedtls/blowfish.h
+++ b/include/mbedtls/blowfish.h
@@ -41,6 +41,7 @@
 #define MBEDTLS_BLOWFISH_BLOCKSIZE   8          /* Blowfish uses 64 bit blocks */
 
 #define MBEDTLS_ERR_BLOWFISH_INVALID_KEY_LENGTH                -0x0016  /**< Invalid key length. */
+#define MBEDTLS_ERR_BLOWFISH_HW_ACCEL_FAILED                   -0x0017  /**< Blowfish hardware accelerator failed. */
 #define MBEDTLS_ERR_BLOWFISH_INVALID_INPUT_LENGTH              -0x0018  /**< Invalid data input length. */
 
 #if !defined(MBEDTLS_BLOWFISH_ALT)