Improve definitions of CPU/PCIe windows for Armada38x

Enhance existing ARMADAXP defines and introduce new MV_WIN_PCIE_
definitions.

Reviewed by: andrew
Obtained from: Semihalf
Sponsored by: Stormshield
Submitted by: Bartosz Szczepanek <bsz@semihalf.com>
Differential revision: https://reviews.freebsd.org/D4378