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

Going forward, struct intel_display is the main device data structure
for display. Convert the power map code to it.

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/9df6b67914cd5afe7107c8431e8c475794b62298.1732808222.git.jani.nikula@intel.com