PCI: Prevent assignment to unsupported bridge windows

Previously, pci_read_bridge_io() and pci_read_bridge_mmio_pref()
unconditionally set resource type flags (IORESOURCE_IO or IORESOURCE_MEM |
IORESOURCE_PREFETCH) when reading bridge window registers. For windows that
are not implemented in hardware, this may cause the allocator to assign
space for a window that doesn't exist.

For example, the EcoNET EN7528 SoC Root Port doesn't support the
prefetchable window, but since a downstream device had a prefetchable BAR,
the allocator mistakenly assigned a prefetchable window:

pci 0001:00:01.0: [14c3:0811] type 01 class 0x060400 PCIe Root Port
pci 0001:00:01.0: PCI bridge to [bus 01-ff]
pci 0001:00:01.0: bridge window [mem 0x28000000-0x280fffff]: assigned
pci 0001:00:01.0: bridge window [mem 0x28100000-0x282fffff pref]: assigned
pci 0001:01:00.0: BAR 0 [mem 0x28100000-0x281fffff 64bit pref]: assigned

pci_read_bridge_windows() already detects unsupported windows by testing
register writability and sets dev->io_window/pref_window accordingly.

Check dev->io_window/pref_window so we don't set the resource flags for
unsupported windows, which prevents the allocator from assigning space to
them.

After this commit, the prefetchable BAR is correctly allocated from the
non-prefetchable window:

pci 0001:00:01.0: bridge window [mem 0x28000000-0x281fffff]: assigned
pci 0001:01:00.0: BAR 0 [mem 0x28000000-0x280fffff 64bit pref]: assigned

Suggested-by: Bjorn Helgaas <helgaas@kernel.org>
Link: https://lore.kernel.org/all/20260113210259.GA715789@bhelgaas/
Signed-off-by: Ahmed Naseef <naseefkm@gmail.com>
Signed-off-by: Caleb James DeLisle <cjd@cjdns.fr>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://patch.msgid.link/20260312165332.569772-4-cjd@cjdns.fr