drm/i915: Remove redundant toggling from the power well sync_hw hooks

Doing an explicit enable/disable in the power well sync_hw hook based on
the power well's reference count is redundant, since by the time these
hooks are called all the power wells are enabled and have a reference.
So remove the redundant toggling.

This is needed by a follow-up patchset that adds power wells which we
can't enable/disable during power domain initialization and so want to
preserve their state until modeset init time.

Cc: Ander Conselvan de Oliveira <conselvan2@gmail.com>
Cc: David Weinehall <david.weinehall@linux.intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Ander Conselvan de Oliveira <conselvan2@gmail.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1487345986-26511-2-git-send-email-imre.deak@intel.com