PM / genirq: Document rules related to system suspend and interrupts
PM / genirq: Document rules related to system suspend and interrupts

Add a document describing how IRQs are managed during system suspend
and resume, how wakeup interrupts work and what the IRQF_NO_SUSPEND
flag is supposed to be used for.

Signed-off-by: Rafael J. Wysocki <27ffc44a8ec6a212fba98cfc3246c6ce8ab131e0@intel.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs