pci_host_generic: Use SYS_RES_MEMORY for the parent of I/O resource ranges

When a SYS_RES_IOPORT resource crosses a pci_host_generic bridge, it
is translated into a memory access for an associated range, so use
SYS_RES_MEMORY for the resource allocated from the parent.

Tested by: markj
Differential Revision: https://reviews.freebsd.org/D44207