amd64: allow the mapping of other regions for efirt

Some BIOSes access data outside of regions marked as "runtime" in their
runtime EFI functions. Allow the mapping and preservation of other
regions through a tunable.

The tunable is a bitmap specifying the regions to map. e.g bit 3 would
be set to map BootServicesCode.

Currently allowed regions are:
BootServicesCode
BootServicesData
RuntimeServicesCode
RuntimeServicesData
ACPIMemoryNVS

PR: 287422
Reviewed by: kib
Approved by: imp (mentor)
Differential Revision: https://reviews.freebsd.org/D51146