PCI: xilinx-nwl: Use INTX instead of legacy

In the xilinx-nwl controller driver, change all use of "legacy" and
"leg" to "intx", to match the term used in the PCI specifications.

Link: https://lore.kernel.org/r/20231122060406.14695-17-dlemoal@kernel.org
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>