Fix pci_host_generic IOPORT

[bz]

Summary

When using IOPORT with pci_host_generic we are missing
setting the rman_end() which leads to end being before
start and thus a signed extended very large number of
size later on, which kva_alloc() will fail upon and we
will panic. Add the missing call.

Debugged with: andrew
Reviewed by:
Sponsored by: DARPA/AFRL
Found: while using virtio with gem5

Test Plan

Botting gem5 x86, armv7, arm64 with virtio/pci disks.

[andrew]

We might also need to update the virtual address, but that doesn't seem to have been an issue so far.