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

Start converting display power domain code to struct
intel_display. Start off with for_each_power_domain_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/d21752baef1cab52ac3bec4f4e1f09f9acd6c1bf.1732808222.git.jani.nikula@intel.com