HID: uclogic: Refactor UGEE v2 string descriptor parsing

The UGEE v2 tablets expose a string descriptor with their capabilities.

Move the code used to parse the descriptors and generate a parameter
list from it to its own function and add KUnit tests to validate the
parser.

Tested-by: Jouke Witteveen <j.witteveen@gmail.com>
Signed-off-by: José Expósito <jose.exposito89@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>