fastmodel: Enable auto bridging and use it to simplify CortexA76x1.

fastmodel: Enable auto bridging and use it to simplify CortexA76x1.

This lets us avoid having to set up bridges for all the different
interrupt signals coming out of the CPU. When we have more cores, like
in the x2, x3, and x4 versions of the CPU, we won't have to have a
set of bridges for each set of signals, and can connect them all to
external ports using array notation, keeping everything simple,
concise, and maintainable.

Change-Id: I1a5f707073868516e93c106dc17d105409de668a
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/21504
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Chun-Chen TK Hsu <chunchenhsu@google.com>
Maintainer: Giacomo Travaglini <giacomo.travaglini@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>