examples/hwapi: Add hwconfig for DragonBoard 410c.

This requires recently added implementation of machine.Pin from
micropython-lib.

examples/hwapi/hwconfig_dragonboard410c.py

+from machine import Pin
+
+# 96Boards/Qualcomm DragonBoard 410c
+# By default, on-board LEDs are controlled by kernel LED driver.
+# To make corresponding pins be available as normal GPIO,
+# corresponding driver needs to be unbound first (as root):
+# echo -n "soc:leds" >/sys/class/leds/apq8016-sbc:green:user1/device/driver/unbind
+# Note that application also either should be run as root, or
+# /sys/class/gpio ownership needs to be changed.
+
+# User LED 1 on gpio21
+LED = Pin(21, Pin.OUT)