KVM: arm64: vgic: Consolidate vgic_allocate_private_irqs_locked()

KVM: arm64: vgic: Consolidate vgic_allocate_private_irqs_locked()

vgic_allocate_private_irqs_locked() calls two helpers, oddly named
vgic_{,v5_}allocate_private_irq().

Not only these helpers don't allocate anything, but they also
contain duplicate init code that would be better placed in the
caller.

Consolidate the common init code in the caller, rename the helpers
to vgic_{,v5_}setup_private_irq(), and pass the irq pointer around
instead of the index of the interrupt.

Reviewed-by: Joey Gouly <joey.gouly@arm.com>
Link: https://lore.kernel.org/r/20260520091949.542365-7-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>