iommu/amd: Add align parameter to alloc_irq_index()

For multi-MSI IRQ ranges the IRQ index needs to be aligned
to the power-of-two of the requested IRQ count. Extend the
alloc_irq_index() function to allow such an allocation.

Reported-by: Thomas Gleixner <tglx@linutronix.de>
Fixes: 2b324506 ('iommu/amd: Add routines to manage irq remapping tables')
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Joerg Roedel <jroedel@suse.de>