pci: Consistently use pci_vf_* for suballocated VF memory resources

Some of the bus resource methods were passing these up to the parent
which triggered rman mismatch assertions in INVARIANTS kernels.

Reported by: kp
Reviewed by: imp
Tested by: kp (earlier version)
Differential Revision: https://reviews.freebsd.org/D45406

(cherry picked from commit 871b33ad65baf07c92cce120a4fc1978c2ed7b3b)