intpm: use MMIO for AMD EFCH CPUs

Recent AMD CPUs (SMBus PCI revision ID >= 0x51) can disable port-mapped
IO and only support memory-mapped IO. In practice this was observed on a
Zen 3 CPU where PMIO reads all returned 0xff. Update the driver to use
MMIO for these processors while continuing to use PMIO by default.

Reviewed by: imp
Pull Request: https://github.com/freebsd/freebsd-src/pull/1437