pciexp: Move PCI path check one level up to pciexp_enable_ltr()
If we have a PCIe root port without `ops_pci` or without
`get_ltr_max_latencies`, the parent device wouldn't be PCI.
Hence, check for a PCI path early.
Change-Id: I358cb6756750bb10d0a23ab7133b917bfa25988b
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/66845
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Jonathan Zhang <jonzhang@fb.com>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>