HID: ft260: add usb hid to i2c host bridge driver

The FTDI FT260 chip implements USB to I2C/UART bridges through two
USB HID class interfaces. The first - for I2C, and the second for UART.
Each interface is independent, and the kernel detects it as a separate
USB hidraw device.

This commit adds I2C host adapter support.

Signed-off-by: Michael Zaidman <michael.zaidman@gmail.com>
Tested-by: Aaron Jones (FTDI-UK) <aaron.jones@ftdichip.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>