amd64 acpi_wakeup: map 1:1 whole low 4G for the trampoline page table

This is required since kernel text might be physically located
anywhere below 4G.

PR: 258432
Reported by: Taku YAMAMOTO <taku@tackymt.homeip.net>
Reviewed by: markj
Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Differential revision: https://reviews.freebsd.org/D31916