ARM GIC specification in device trees use 3 cells, so the current
limit of 2 causes the last cell to be dropped. This in turn can
cause the interrupt polarity and trigger settings to be incorrect.
Increase the limit to 4 which should handle all reasonable cases.
This fixes issues seen in QEMU when registering PCI interrupts.
FDT attachment to a new file. A separate ACPI attachment will then be added
to allow arm64 servers with ACPI to use it over FDT.
This should also help with merging this with the ofwpci driver, with
further work needed to remove restrictions this driver places on resource
allocation.
Obtained from: ABT Systems Ltd
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D7319