Only the GICv3 model has a `gicv4` parameter, causing the current `baremetal.py` config to throw an exception when used with the VExpress_GEM5_V1 platform containing a GICv2. This patch checks for the existence of the `gicv4` parameter, allowing all VExpress platforms to be used. Change-Id: I72667a9caee64fa497bda516217cd424050eb242 Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/69685 Tested-by: kokoro <noreply+kokoro@google.com> Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com> Maintainer: Giacomo Travaglini <giacomo.travaglini@arm.com>