linuxkpi: Fix PCI BAR lazy allocation support.

FreeBSD supports lazy allocation of PCI BAR, that is, when a device
driver's attach method is invoked, even if the device's PCI BAR
address wasn't initialized, the invocation of bus_alloc_resource_any()
(the call chain: pci_alloc_resource() -> pci_alloc_multi_resource() ->
pci_reserve_map() -> pci_write_bar()) would allocate a proper address
for the PCI BAR and write this 'lazy allocated' address into the PCI
BAR.

This model works fine for native FreeBSD device drivers, but _not_ for
device drivers shared with Linux (e.g. dev/mlx5/mlx5_core/mlx5_main.c
and ofed/drivers/net/mlx4/main.c.  Both of them use
pci_request_regions(), which doesn't work properly with the PCI BAR
lazy allocation, because pci_resource_type() -> _pci_get_rle() always
returns NULL, so pci_request_regions() doesn't have the opportunity to
invoke bus_alloc_resource_any().  We now use pci_find_bar() in
pci_resource_type(), which is able to locate all available PCI BARs
even if some of them will be lazy allocated.

Submitted by:   Dexuan Cui <decui microsoft com>
Reviewed by:    hps
Sponsored by:   Microsoft
Differential Revision:  https://reviews.freebsd.org/D8071