arch-arm, kvm: Fix KVM_ARM_IRQ_VCPU2_SHIFT compilation error

After the following patch:

https://gem5-review.googlesource.com/c/public/gem5/+/59310

gem5 doesn't compile on Arm machines that don't define the
KVM_ARM_IRQ_VCPU2_SHIFT macro as the latter is not guarded anymore.

This patch fixes the problem by amending capIRQLineLayout2 to
rely on KVM_CAP_ARM_IRQ_LINE_LAYOUT_2 only (which makes
sense) and moves back the KVM_ARM_IRQ_VCPU2_SHIFT guard
back to its original place

Change-Id: Ib6b6ef4014c2a54580cb3e5b0167d4ee1f7139ed
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/63111
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>
2 files changed