drm/i915: Remove DSPARB_HWCONTROL()

This define hasn't been used since:

  commit 652c393a
  Author: Jesse Barnes <jbarnes@virtuousgeek.org>
  Date:   Mon Aug 17 13:31:43 2009 -0700

      drm/i915: add dynamic clock frequency control

Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>