Spresense exported SDK

Prepared and exported Spresense SDK. To reproduce this, follow the steps below.

Step 1 - Clone Spresense SDK

$ git clone --recursive https://github.com/sonydevworld/spresense.git
$ cd spresense/sdk

Step 2 - Configure Spresense SDK

$ tools/config.py -d <path to CircuitPython>/ports/cxd56 circuitpython

Step 3 - Build and export Spresense SDK

$ make
$ make exportsdk

Step 4 - Extract Spresense SDK and change the name of the folder

$ unzip sdk-export.zip
$ mv sdk-export spresense-exported-sdk

Step 5 - Modify Spresense SDK

In file spresense-exported-sdk/nuttx/include/nuttx/fs/fs.h (line 817) comment

// int file_open(FAR struct file *filep, FAR const char *path, int oflags, ...);