The string descriptor returned by UGEE v2 devices contains a byte
indicating the device frame type.

The values discovered so far are:

 - 0: Frame with buttons, present in the XP-PEN Deco L.
 - 1: Frame with buttons and dial, present in the PARBLO A610 PRO.
 - 2: Frame with buttons and a mouse, shaped as a dial + touchpad.
      Present in the XP-PEN Deco Pro S.

Parse the frame type and add KUnit tests.
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>