Map arm64 pci config memory as non-posted

On arm64 PCI config memory is expected to be mapped with a non-posted
device type. To handle this use the new bus_map_resource support in
arm64 to map memory with the new VM_MEMATTR_DEVICE_NP attribute. This
memory has already been allocated and activated, it just needs to be
mapped.

Reviewed by: kevans, mmel
Differential Revision: https://reviews.freebsd.org/D30079