drm/i915/display: convert for_each_power_well() to struct intel_display

Start converting power well code to struct intel_display. Start off with
for_each_power_well() and the reverse variant.

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/30c3e44cdb9557a195b2e086bf169da8d8497c6b.1732808222.git.jani.nikula@intel.com