KVM: arm64: selftests: vgic_irq: Add asymmetric SPI deaectivation test

KVM: arm64: selftests: vgic_irq: Add asymmetric SPI deaectivation test

Add a new test case that makes an interrupt pending on a vcpu,
activates it, do the priority drop, and then get *another* vcpu
to do the deactivation.

Special care is taken not to trigger an exit in the process, so
that we are sure that the active interrupt is in an LR. Joy.

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/20251120172540.2267180-48-maz@kernel.org
Signed-off-by: Oliver Upton <oupton@kernel.org>