KVM: selftests: aarch64: Cmdline arg to set number of IRQs in vgic_irq test

Add the ability to specify the number of vIRQs exposed by KVM (arg
defaults to 64). Then extend the KVM_IRQ_LINE test by injecting all
available SPIs at once (specified by the nr-irqs arg). As a bonus,
inject all SGIs at once as well.

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/20211109023906.1091208-9-ricarkol@google.com