KVM: selftests: Add kvm_irq_line library function

Add an architecture independent wrapper function for the KVM_IRQ_LINE
ioctl.

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/20211109023906.1091208-5-ricarkol@google.com