CHROMEOS: HID: Helper functions for Logitech HID++

CHROMEOS: HID: Helper functions for Logitech HID++

This is part of the next iteration of Nestor Lopez Casado's
introduction of HID++ support to the kernel from his patch "[PATCH
1/1] HID: Add full MT support for Logitech Wireless Touchpad"

HID++ is a Logitech-specific protocol for communicating with HID
devices. It can be used, for example, to probe properties of devices
(like touch surface dimensions, battery status, and more), and to set
state on a device (like a request to put the device into raw mode).

Documentation is provided at
https://drive.google.com/a/logitech.com/?tab=mo#folders/0BxbRzx7vEV7eWmgwazJ3NUFfQ28

BUG=chromium-os:39354
TEST=manually tested on Link

Signed-off-by: Andrew de los Reyes <adlr@chromium.org>
Change-Id: I1b87558cc31cb77ef277820f0b00f3ea6e1b367e
Reviewed-on: https://gerrit.chromium.org/gerrit/46009
Reviewed-by: Yufeng Shen <miletus@chromium.org>