Implement workaround for Armada 38X family HW issue between CPU and devices

There is a hardware problem between Cortex-A9 CPUs and on-chip devices
in Armada 38X SoCs that may cause hang on heavy load. This can be
however worked around by mapping all registers and PCI IO
as strongly ordered instead of device memory.

Submitted by: Zbigniew Bodek <zbb@semihalf.com>
Reviewed by: mmel
Tested by: mw_semihalf.com
Obtained from: Semihalf
Differential revision: https://reviews.freebsd.org/D10218