Support for MSI-X on Annapurna Alpine

This patch adds support for MSI-X interrupts
on Annapurna Alpine platform. MSI-X on Alpine
work similarly to GICv2m, i.e. some range of
SPI interrupts is reserved in GIC and individual
SPIs can be triggered by MSI-X messages.
This SPI range is defined in FDT.

Obtained from: Semihalf
Submitted by: Michal Stanek <mst@semihalf.com>
Sponsored by: Annapurna Labs
Reviewed by: nwhitehorn, wma
Differential Revision: https://reviews.freebsd.org/D7579