oxnas: finally make board names consistent

r48337 unfortunately incorrectly changed the boardname of the stg212
into stg-212 which is not the name of the image of DTS file or
boardname using sysupgrade, which is 'stg212' and imho should stay
that way.
The changes r48337 made for pogoplug-pro and pogoplug-v3 were correct,
thus this commit only partially reverts r48337.
Also properly set default for USB LED while already at it.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

SVN-Revision: 48398