irqchip/gic-v3-its: Remove ACPICA version check for ACPI NUMA

The version check was added due to dependency to

 a618c7f8 ACPICA: Add support for new SRAT subtable

Now, that this code is in the kernel, remove the check. This is esp.
useful to enable backports.

Signed-off-by: Robert Richter <rrichter@cavium.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>