drm/i915: Respin vlv/chv reagister access to look more like SKL

drm/i915: Respin vlv/chv reagister access to look more like SKL

Change the fw domain handling in the vlv/chv register read/write
functions to look more like the SKL code, ie. have a single
__force_wake_get() get call instead of multiple ones.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1445517300-28173-5-git-send-email-ville.syrjala@linux.intel.com
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>