PCI: pciehp: Enable by default if USB4 enabled

Thunderbolt/USB4 PCIe tunneling depends on native PCIe hotplug.  Enable
pciehp by default if USB4 is enabled.

[bhelgaas: squash, update subject, commit logs, tidy whitespace]
Link: https://lore.kernel.org/r/20221115113857.35800-2-albert.zhou.50@gmail.com
Link: https://lore.kernel.org/r/20221115113857.35800-3-albert.zhou.50@gmail.com


Signed-off-by: Albert Zhou <albert.zhou.50@gmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>