drm/i915: Use generic vblank wait

This has the upside that it will no longer steal interrupts from the
interrupt handler on pre-g4x. Furthermore this will now scream properly
on all platforms if we don't have hw counters enabled.

v2: Adjust to the new names.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>