Add w1-ds18b20 (#1659)

Author: dimerr

general/package/w1-ds18b20/Config.in

@@ -0,0 +1,4 @@
+config BR2_PACKAGE_W1-DS18B20
+	bool "w1-ds18b20"
+	help
+	  OneWire DS18B20 GPIO bitbang app

general/package/w1-ds18b20/readme.md

@@ -0,0 +1,13 @@
+# w1-ds18b20
+
+This app allows reading ds18b20 sensors in bitbang mode using direct GPIO memory access.
+Currently supports only HiSilicon-style GPIO offsets. Pull-up resistor is required.
+
+## Usage
+
+Example: reading temperature using GPIO8_2 on Gk7205V300 (consult datasheet or ipctool output)
+
+```
+# ./w1-ds18b20 -base 0x120B8000 -gpio 2
+28-4A4E3C1E64FF :  22.44 C
+```