Instead of making multiple calls to pcibios_get_irq_routing_table, let's
just do it once and save the answer.

The reason we were making multiple calls is because we liked to calculate
its length and perform some loop over it. Instead of open-coding the length
calculation every time, provide it in an inline helper function.

Finally, since pci_print_IRQ_route() is used only for debug, let's only
do it when cpqhp_debug is set.
Signed-off-by: Alex Chiang <achiang@hp.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>