Add api for creating resource list based on 'assigned-addresses'

According to device tree binding 'assigned-addresses' can refer to PCIE MMIO
register space. New function ofw_bus_assigned_addresses_to_rl is
provided to support it.

Submitted by: Rafal Kozik <rk@semihalf.com>
Obtained from: Semihalf
Sponsored by: Stormshield
Differential Revision: https://reviews.freebsd.org/D14750