smdk4x12-common: fix bt tether

Change-Id: Ib19439e39ba767e57826722279faaed02046df2e
Get rid of the gfx buffer workarounds

Concurrent buffers are now working, we don't need this crap anymore

Change-Id: I80c35bb67c41e9c61faeb6f3cd80d3e9033f9641