esp32c6: Enable ECDSA based secure boot

- Updated documentation for C6

components/esp_rom/include/esp32c6/rom/ecdsa.h

@@ -0,0 +1,26 @@
+/*
+ * SPDX-FileCopyrightText: 2021-2022 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#pragma once
+
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#define ETS_DIGEST_LEN 32 /* SHA-256, bytes */
+
+typedef enum {
+    ECDSA_CURVE_P192 = 1,
+    ECDSA_CURVE_P256 = 2
+} ECDSA_CURVE;
+
+int ets_ecdsa_verify(const uint8_t *key, const uint8_t *sig, ECDSA_CURVE curve_id, const uint8_t *digest, uint8_t *verified_digest);
+
+#ifdef __cplusplus
+}
+#endif