boot/espressif: Add CMakeLists.txt and mcuboot_config.h

Add sources and headers required for build

Signed-off-by: Shubham Kulkarni <shubham.kulkarni@espressif.com>
diff --git a/boot/espressif/main.c b/boot/espressif/main.c
new file mode 100644
index 0000000..9b98fbf
--- /dev/null
+++ b/boot/espressif/main.c
@@ -0,0 +1,18 @@
+/*
+ * Copyright (c) 2021 Espressif Systems (Shanghai) Co., Ltd.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <bootutil/bootutil.h>
+
+int main()
+{
+    struct boot_rsp rsp;
+    int rv = boot_go(&rsp);
+
+    if (rv == 0) {
+        //    
+    }
+    while(1);
+}