drm/i915/display: convert power wells to struct intel_display

Going forward, struct intel_display is the main device data structure
for display. Switch the power well code over to it.

v2: Fix parenthesis alignment

Cc: Imre Deak <imre.deak@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/b8c0ff5502a5df55ec7a160d90257c6f2befc0b6.1732808222.git.jani.nikula@intel.com