hid: Import iichid - I2C transport backend for HID subsystem

This implements hid_if.m methods for HID-over-I2C protocol [1].

Following kernel options are added:

IICHID_SAMPLING - Enable support for a sampling mode as interrupt

resource acquisition is not always possible in a case
of GPIO interrupts.

IICHID_DEBUG - Enable debug output.

The module is based on prior Marc Priggemeyer work (D16698).

[1] http://download.microsoft.com/download/7/d/d/7dd44bb7-2a7a-4505-ac1c-7227d3d96d5b/hid-over-i2c-protocol-spec-v1-0.docx

Differential revision: https://reviews.freebsd.org/D27892