acpi: Parse _S3D in s2idle instead of _S255D

Previously, when entering s2idle, we were parsing the _S255D object to
get the shallowest D-state supported by device, as
acpi_stype_to_sstate() returns -1 for s2idle.

Instead, we should read _S3D.

Relevant document:
https://uefi.org/htmlspecs/ACPI_Spec_6_4_html/07_Power_and_Performance_Mgmt/device-power-management-objects.html#s3d-s3-device-state

Reviewed by: olce
Tested by: emaste, olce
Approved by: olce
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D55118