soc: qcom: smp2p: Add proper retrigger detection

Currently, smp2p relies on the hwirq resend feature to retrigger irqs
that were missed because the irq was disabled at the time of receiving
it. The hwirq resend feature will retrigger the parent smp2p interrupt.
In order to keep track of what children needed to be retriggered, the
pending bitmap was added.

After calling handle_nested_irq, smp2p checks if the interrupt is
enabled and sets the pending bit if the interrupt is not enabled. There
is a small window where a client can enable the interrupt between
calling handle_nested_irq and checking if the interrupt is enabled.
If this happens, the interrupt is never called when the parent smp2p
interrupt is retriggered.

Add the irq_retrigger callback so smp2p can know which child interrupts
need to be retriggered. Set the pending bits accordingly.

Change-Id: I774b6ef91e22edbd55ddfffbbb3ae6062d48a560
Signed-off-by: Chris Lew <clew@codeaurora.org>