KVM: arm64: selftests: vgic_irq: Add timer deactivation test

KVM: arm64: selftests: vgic_irq: Add timer deactivation test

Add a new test case that triggers the HW deactivation emulation path
when trapping ICV_DIR_EL1. This is obviously tied to the way KVM
works now, but the test follows the expected architectural behaviour.

Tested-by: Fuad Tabba <tabba@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Tested-by: Mark Brown <broonie@kernel.org>
Link: https://msgid.link/20251120172540.2267180-50-maz@kernel.org
Signed-off-by: Oliver Upton <oupton@kernel.org>