Reenable metronome on Archos targets which got lost during the big change to it in...

Reenable metronome on Archos targets which got lost during the big change to it in last summer and fix a warning (wrong data type). The plugin button action system causes problems with the Ondio controls (tapping and playing conflict, even though there are exceptions defined) and it's only halfway usable, probably this applies to the Player as well but couldn't test. It is still better than nothing and e.g. metronome is not completely controllable on c200 too  where it is also enabled.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@16079 a1c6a512-1295-4272-9138-f99709370657