drm/radeon/kms: use new pre/post_xfer i2c bit algo hooks

This allows us to remove the internal bit algo bus used by
the radeon i2c algo.  We now register a radeon algo adapter
if the gpio line is hw capable and the hw inplementation is
available, otherwise we register a bit algo adapter.

Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>