PCI: keystone: Use INTX instead of legacy

In the Keystone controller driver, change all names using "legacy" to
use "intx" instead, to match the term used in the PCI specifications.
Given that the field legacy_intc_np of struct keystone_pcie is unused,
this field is removed instead of being renamed.

Link: https://lore.kernel.org/r/20231122060406.14695-11-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>