acpi_pci: Cache PCI proximity domains

[kbowling]

Summary

A PCI function's _PXM is stable for the lifetime of its device
instance, but CPU and DMA locality queries may evaluate it repeatedly.
SR-IOV amplifies this because every VF resolves locality through the
same PF.

Cache successful mappings and the stable absence of _PXM on the
locality source device, and share that result between CPU and domain
queries. Continue to retry generic evaluation or mapping errors rather
than making a potentially transient failure permanent.

MFC after:      2 weeks