arm64: Increase NIRQ to 16k

[scottph]

Summary

Ampere Altra in a dual socket configuration has 12 ITSes for the
12 PCIe root complexes. The NIRQ interrupts are statically split
between each child of the gic bus, so we need to increase that
value. 16k is enough for

(#cpus * #its * max_pcie_bifurcation) LPIs + (#SPIs and #PPIs)

Sponsored by: Ampere Computing

[scottph]

This increases bss by ~1.5 MiB

[jhb]

If possible, I would encourage you to explore making these things tunable and more dynamic ala rS338360, rS340460, and rS340488.