Cavium ThunderX2 SMMU doesn't support MSI and also doesn't have unique irq
lines for gerror, eventq and cmdq-sync.

New named irq "combined" is set as a errata workaround, which allows to
share the irq line by register single irq handler for all the interrupts.
Acked-by: NLorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: NGeetha sowjanya <gakula@caviumnetworks.com>
[will: reworked irq equality checking and added SPI check]
Signed-off-by: NWill Deacon <will.deacon@arm.com>