Add IOT2050 board into mraa Intel nodes (#940)

* mraa-gpio-led: add led

This patch introduces LED node in GPIO category.

Signed-off-by: zengchao <chao.zeng@siemens.com>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Ivan Mikhaylov <ivan.mikhaylov@siemens.com>

* mraa-gpio-ain: add iot2050 board

Add IOT2050 board in list of possible boards.

Signed-off-by: zengchao <chao.zeng@siemens.com>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Ivan Mikhaylov <ivan.mikhaylov@siemens.com>

* mraa-gpio-dout: add iot2050 board

Add IOT2050 board into list of possible boards.

Signed-off-by: zengchao <chao.zeng@siemens.com>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Ivan Mikhaylov <ivan.mikhaylov@siemens.com>

* mraa-gpio-pwm: add iot2050 board

Add IOT2050 board into list of possible boards.

Signed-off-by: zengchao <chao.zeng@siemens.com>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Ivan Mikhaylov <ivan.mikhaylov@siemens.com>

* mraa-gpio: clean up on close for ain, pwm, dout

Required as nodejs will only lazily delete the node objects, and we may
race with the next user requesting the resources.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Ivan Mikhaylov <ivan.mikhaylov@siemens.com>

* mraa-gpio-din: add USER button

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

Signed-off-by: zengchao <chao.zeng@siemens.com>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Ivan Mikhaylov <ivan.mikhaylov@siemens.com>
Co-authored-by: Jan Kiszka <jan.kiszka@siemens.com>

hardware/intel/mraa-gpio-din.html

@@ -68,6 +68,7 @@
             <option value="17">D17</option>
             <option value="18">D18</option>
             <option value="19">D19</option>
+            <option value="20">USER button</option>
         </select>
     </div>
     <div class="form-row">