[acpi] Change MapResource to be in line with pdev and pci mmio APIs.

Mapping the resource across banjo protocols assumes both drivers are in
the same process. Although that works currently, it shouldn't be the
long term plan to keep ACPI children in the same devhost as the ACPI
driver itself.

Tested: booted pixelbook
Change-Id: I1786ba61e91c38b31fc65d41b829fc31d9f99621