spmi: pmic_arb: add interrupt support to virtio spmi

Add another virtio queue to receive irq notification from
spmi backend. The virtio spmi controller is also a hierarchy
irqchip to handle pmic client interrupts.

Change-Id: I98f44492982340286b68a97537189c3b57c9cd5b
Signed-off-by: Yimin Peng <yiminp@codeaurora.org>