drm/i915: Move hsw_power_well_enable() next to the rest of HSW helpers

Move the helper next to the rest of HSW specific code.

Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Arkadiusz Hiler <arkadiusz.hiler@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1499352040-8819-18-git-send-email-imre.deak@intel.com


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