This is a follow-on to 'vPCI: avoid bogus "overlap in extended cap list"
warnings', addressing further issues noted there.

v5: One new patch and some other re-work. See individual patches.

1: introduce private header
2: move vpci_init_capabilities() to a separate file
3: move capability-list init
4: ReBAR: improve cleanup
5: re-init extended-capabilities when MMCFG availability changed

Jan