Deprecate hardware acceleration errors

Deprecate the module-specific XXX_HW_ACCEL_FAILED and
XXX_FEATURE_UNAVAILABLE errors, as alternative implementations should now
return `MBEDTLS_ERR_PLATFORM_HW_FAILED` and
`MBEDTLS_ERR_PLATFORM_FEATURE_UNSUPPORTED`.
diff --git a/include/mbedtls/cmac.h b/include/mbedtls/cmac.h
index a4fd552..c196793 100644
--- a/include/mbedtls/cmac.h
+++ b/include/mbedtls/cmac.h
@@ -34,6 +34,7 @@
 extern "C" {
 #endif
 
+/* MBEDTLS_ERR_CMAC_HW_ACCEL_FAILED is deprecated and should not be used. */
 #define MBEDTLS_ERR_CMAC_HW_ACCEL_FAILED -0x007A  /**< CMAC hardware accelerator failed. */
 
 #define MBEDTLS_AES_BLOCK_SIZE          16