make bootloader_support depend on IDF_TARGET

1. move chip-specific code(e.g. encryption) into IDF_TARGET directory
2. splict app-only code to idf directory which won't be compiled into bootloader

components/bootloader_support/src/idf/bootloader_sha.c

@@ -0,0 +1,53 @@
+// Copyright 2017 Espressif Systems (Shanghai) PTE LTD
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+#include "bootloader_sha.h"
+#include <stdbool.h>
+#include <string.h>
+#include <assert.h>
+#include <sys/param.h>
+#include <mbedtls/sha256.h>
+
+bootloader_sha256_handle_t bootloader_sha256_start()
+{
+    mbedtls_sha256_context *ctx = (mbedtls_sha256_context *)malloc(sizeof(mbedtls_sha256_context));
+    if (!ctx) {
+        return NULL;
+    }
+    mbedtls_sha256_init(ctx);
+    int ret = mbedtls_sha256_starts_ret(ctx, false);
+    if (ret != 0) {
+        return NULL;
+    }
+    return ctx;
+}
+
+void bootloader_sha256_data(bootloader_sha256_handle_t handle, const void *data, size_t data_len)
+{
+    assert(handle != NULL);
+    mbedtls_sha256_context *ctx = (mbedtls_sha256_context *)handle;
+    int ret = mbedtls_sha256_update_ret(ctx, data, data_len);
+    assert(ret == 0);
+}
+
+void bootloader_sha256_finish(bootloader_sha256_handle_t handle, uint8_t *digest)
+{
+    assert(handle != NULL);
+    mbedtls_sha256_context *ctx = (mbedtls_sha256_context *)handle;
+    if (digest != NULL) {
+        int ret = mbedtls_sha256_finish_ret(ctx, digest);
+        assert(ret == 0);
+    }
+    mbedtls_sha256_free(ctx);
+    free(handle);
+}