KVM: selftests: aarch64: Add vgic_irq to test userspace IRQ injection

Add a new KVM selftest, vgic_irq, for testing userspace IRQ injection.  This
particular test injects an SPI using KVM_IRQ_LINE on GICv3 and verifies
that the IRQ is handled in the guest. The next commits will add more
types of IRQs and different modes.

Signed-off-by: Ricardo Koller <ricarkol@google.com>
Acked-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20211109023906.1091208-7-ricarkol@google.com