libpci: win32-cfgmgr32: Add support for accessing config space via other backend

libpci: win32-cfgmgr32: Add support for accessing config space via other backend

Extend win32-cfgmgr32 backend and add a new option win32.cfgmethod for
specifying other backend for accessing PCI config space. There are more
config space access methods available on Windows and each is working only
sometimes (either requires special privileges or special setup).

So by default try to choose the first working one via order defined in pci
probe_sequence[] array. If none is available then emulate PCI config space
like before this change.

Function pci_init_v35() is extended and renamed to pci_init_internal() to
optionally do not throw errors and allow to specify one access method which
will be skipped in AUTO mode. This is used to prevent choosing win32-cfgmgr32
as config space access method for win32-cfgmgr32.