misc: Add Giacomo Travaglini as an Arm maintainer

misc: Add Giacomo Travaglini as an Arm maintainer

I have been delegating a lot of changes to Giacomo T for a long time,
making him a de facto Arm co-maintainer. Make this official by adding
him to the list of maintainers.

Change-Id: I69c53316e2fc6ca162d07ac2d167ac2ae2b6bbee
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/21899
Maintainer: Jason Lowe-Power <jason@lowepower.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>