Adding support for HID over I2C and uhid devices

[haata]

• uhid USB, Bluetooth (standard) and I2C now enumerating
  • USB uhid support was added by removing the udev USB endpoint check
• HID over I2C was excluded before (likely because it didn't exist when
  hidraw was developed)

I'm still looking for a device with HID over I2C (I have one
somewhere...). For now I've tested that code path using uhid instead.

Device Found
type: 308f 0030
path: /dev/hidraw14
serial_number: uhid virtual
Manufacturer:
Product: HID-IO Virtual Keyboard - Standard USB
Release: 0
Interface: -1
Usage (page): 0x6 (0x1)

Device Found
type: 308f 0030
path: /dev/hidraw17
serial_number: uhid virtual
Manufacturer:
Product: HID-IO Virtual Keyboard - Standard I2C
Release: 0
Interface: -1
Usage (page): 0x6 (0x1)

[Youw]

LGTM
Although, I cannot check or verify any of this.
Would be great if someone could check it just to confirm.

[haata]

I added a few more changes (forgot about the get_device_string function), after I did some more integration testing.

Thanks for reviewing!

If anyone would like to test the uhid part, a very easy way is to build this uhid-virt example https://github.com/haata/uhid-virt/tree/master/example; you'll need to run the executable as root though.

cargo build
sudo target/debug/example

Pressing enter while running will move the mouse.
Ctrl-C to exit.
(it's just a rust version of the Linux kernel uhid example code https://github.com/torvalds/linux/blob/master/samples/uhid/uhid-example.c; but it's a bit easier to setup if you already have rust on your system).

The HID over I2C is a bit trickier unfortunately.

[haata]

Cleaned up code formatting.

[Youw]

@haata do you have anything to add to this PR? I think it is ready to be merged

[haata]

I think everything is still good. I've been running with these changes for quite a while now and haven't had any issues.