genirq: Add chip_[suspend|resume] PM support to irq_chip

genirq: Add chip_[suspend|resume] PM support to irq_chip

Some (admittedly odd) irqchips perform functions that are not directly
related to any of their child IRQ lines, and therefore need to perform
some tasks during suspend/resume regardless of whether there are
any "installed" interrupts for the irqchip. However, the current
generic-chip framework does not call the chip's irq_{suspend,resume}
when there are no interrupts installed (this makes sense, because there
are no irq_data objects for such a call to be made).

More specifically, irq-bcm7120-l2 configures both a forwarding mask
(which affects other top-level GIC IRQs) and a second-level interrupt
mask (for managing its own child interrupts). The former must be
saved/restored on suspend/resume, even when there's nothing to do for
the latter.

This patch adds a new set of suspend/resume hooks to irq_chip_generic,
to help represent *chip* suspend/resume, rather than IRQ suspend/resume.
These callbacks will always be called for an IRQ chip (regardless of the
installed interrupts) and are based on the per-chip irq_chip_generic
struct, rather than the per-IRQ irq_data struct.

The original problem report is described in extra detail here:
http://lkml.kernel.org/g/20150619224123.GL4917@ld-irv-0074

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Tested-by: Florian Fainelli <f.fainelli@gmail.com>
Cc: Gregory Fong <gregory.0xf0@gmail.com>
Cc: bcm-kernel-feedback-list@broadcom.com
Cc: linux-mips@linux-mips.org
Cc: Kevin Cernekee <cernekee@chromium.org>
Cc: Jason Cooper <jason@lakedaemon.net>
Link: http://lkml.kernel.org/r/1437607300-40858-1-git-send-email-computersforpeace@gmail.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>