Add support for Dial status LEDs

[whot]

libinput at least uses the status leds for grouping: our data file says there's a status led for the ring and the toggle button for the ring is B, and button are at position P. libinput then uses the fact that there are two status LEDs to create two groups and matches the buttons with the position of the mode toggle button (i.e. if button B is in position P, all buttons in the same position P must belong to the same mode group).

This requires that the status led for dials exists, so let's add them.

Fixes: https://github.com/linuxwacom/libwacom/commit/b6b82e4afa6a2114afc819cddf6b3ee65dff2e15 ("Add support for relative dials (https://github.com/linuxwacom/libwacom/pull/665)")