gpio: Add support for hierarchical IRQ domains

Hierarchical IRQ domains can be used to stack different IRQ controllers
on top of each other. One specific use-case where this can be useful is
if a power management controller has top-level controls for wakeup
interrupts. In such cases, the power management controller can be a
parent to other interrupt controllers and program additional registers
when an IRQ has its wake capability enabled or disabled.

Change-Id: I3f63cb13c0cd1b602d3205c40648d5e7d3c62d4d
Patch-mainline: https://lore.kernel.org/patchwork/patch/989528/


Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Lina Iyer <ilina@codeaurora.org>