system-arm: Add ITS node in platforms/vexpress_gem5_v2_base.dtsi
system-arm: Add ITS node in platforms/vexpress_gem5_v2_base.dtsi

This is aligning sources with DTB autogeneration

Change-Id: Icf369eb85719c91da770398b45645d8b03d8abf3
Reviewed-by: Andreas Sandberg <c9f5686ee5bd561c93f9de79681eee75bfa7f36e@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/20982
Maintainer: Andreas Sandberg <c9f5686ee5bd561c93f9de79681eee75bfa7f36e@arm.com>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5