drm/i915/hsw, bdw: Remove redundant state check during power well toggling

Similarly to the GEN9 power well toggling, saving an occasional extra
MMIO write is not worth the code complexity, let's simplify things.

Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Arkadiusz Hiler <arkadiusz.hiler@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1499352040-8819-11-git-send-email-imre.deak@intel.com


Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>