fix(mbedtls/gcm): Add support for software fallback for non-AES ciphers in a GCM operation

- Even if the config MBEDTLS_HARDWARE_AES is enabled, we now support fallback
to software implementation of GCM operations when non-AES ciphers are used.

components/mbedtls/port/include/mbedtls/esp_config.h

@@ -155,6 +155,12 @@
 
 #ifdef CONFIG_MBEDTLS_HARDWARE_AES
 #define MBEDTLS_GCM_ALT
+#ifdef CONFIG_MBEDTLS_GCM_SUPPORT_NON_AES_CIPHER
+    /* Prefer hardware and fallback to software */
+    #define MBEDTLS_GCM_NON_AES_CIPHER_SOFT_FALLBACK
+#else
+    #undef MBEDTLS_GCM_NON_AES_CIPHER_SOFT_FALLBACK
+#endif
 #endif
 
 /* MBEDTLS_SHAxx_ALT to enable hardware SHA support

components/mbedtls/port/include/mbedtls/gcm.h

@@ -0,0 +1,81 @@
+/*
+ * SPDX-FileCopyrightText: 2023-2024 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+#pragma once
+
+#include_next "mbedtls/gcm.h"
+#include "sdkconfig.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#if defined(MBEDTLS_GCM_ALT) && defined(MBEDTLS_GCM_NON_AES_CIPHER_SOFT_FALLBACK)
+
+/**
+ * When the MBEDTLS_GCM_NON_AES_CIPHER_SOFT_FALLBACK is defined, for non-AES GCM
+ * operations we need to fallback to the software function definitions of the
+ * mbedtls GCM layer.
+ * Thus in this case we need declarations for the software funtions.
+ * Please refer mbedtls/include/mbedtls/gcm.h for function documentations
+ */
+
+void mbedtls_gcm_init_soft(mbedtls_gcm_context_soft *ctx);
+
+
+int mbedtls_gcm_setkey_soft(mbedtls_gcm_context_soft *ctx,
+                            mbedtls_cipher_id_t cipher,
+                            const unsigned char *key,
+                            unsigned int keybits);
+
+int mbedtls_gcm_starts_soft(mbedtls_gcm_context_soft *ctx,
+                            int mode,
+                            const unsigned char *iv, size_t iv_len);
+
+int mbedtls_gcm_update_ad_soft(mbedtls_gcm_context_soft *ctx,
+                            const unsigned char *add, size_t add_len);
+
+int mbedtls_gcm_update_soft(mbedtls_gcm_context_soft *ctx,
+                            const unsigned char *input, size_t input_length,
+                            unsigned char *output, size_t output_size,
+                            size_t *output_length);
+
+int mbedtls_gcm_finish_soft(mbedtls_gcm_context_soft *ctx,
+                            unsigned char *output, size_t output_size,
+                            size_t *output_length,
+                            unsigned char *tag, size_t tag_len);
+
+
+int mbedtls_gcm_crypt_and_tag_soft(mbedtls_gcm_context_soft *ctx,
+                                int mode,
+                                size_t length,
+                                const unsigned char *iv,
+                                size_t iv_len,
+                                const unsigned char *add,
+                                size_t add_len,
+                                const unsigned char *input,
+                                unsigned char *output,
+                                size_t tag_len,
+                                unsigned char *tag);
+
+
+int mbedtls_gcm_auth_decrypt_soft(mbedtls_gcm_context_soft *ctx,
+                                size_t length,
+                                const unsigned char *iv,
+                                size_t iv_len,
+                                const unsigned char *add,
+                                size_t add_len,
+                                const unsigned char *tag,
+                                size_t tag_len,
+                                const unsigned char *input,
+                                unsigned char *output);
+
+void mbedtls_gcm_free_soft(mbedtls_gcm_context_soft *ctx);
+
+#endif /* MBEDTLS_GCM_ALT && MBEDTLS_GCM_NON_AES_CIPHER_SOFT_FALLBACK*/
+
+#ifdef __cplusplus
+}
+#endif