Add driver for temperature/humidity sensor DHT11 to expose data via sysctl

[mizhka]

Summary

Hi,

This patch adds driver for temperature/humidity sensor connected via GPIO. It called gpioths. Just add "device gpioths" into kernel and hints like:

# Temp/Humidity sensors
hint.gpioths.0.at="gpiobus0"
hint.gpioths.0.pins=1

As results it will provide temperature/humidity values via sysctl:

dev.gpioths.0.temperature: 28
dev.gpioths.0.humidity: 31

DHT11 is cheap & popular temperature/humidity sensor and there is significant amount of blog posts how to meet freebsd & DHT11 (last dated by today, Jan14). It's really worth to bring support into tree. DHT11 is single-wire sensor. It can be connected via GPIO to device like Raspberry Pi or Onion Omega.

Missing bits:

• man page

Test Plan

Tested on Onion Omega & DHT11