device-kobo-clara: add mesa-dri-gallium dep

Mesa dependency was missing causing the screen to stay blank after boot.

Reported on Matrix:

Hi, I'm looking for some support setting up pmOS on my Kobo Clara HD. Is someone here who has some experience with it?

At boot, the screen is cleared (black, then white) but then it remains blank. The waveform is in its place in /lib/... and I've diffed the file against one that I manually extracted (same).

It actually seems to boot into X, too.

My logs are here: http://ix.io/450t (Xorg.0.log) http://ix.io/450u (dmesg)

They installed the mesa-dri-gallium package manually and then the device booted.