PCI: Add support for PCIe WAKE# interrupt

According to PCIe r7.0, sec 5.3.3.2, two link wakeup mechanisms are
defined: Beacon and WAKE#. Beacon is a hardware-only mechanism and is
invisible to software (sec 4.2.7.8.1). This change adds support for the
WAKE# mechanism in the PCI core.

According to the PCIe specification, multiple WAKE# signals can exist in a
system or several components in the hierarchy may share a single WAKE#
signal. In configurations involving a PCIe switch, each downstream port
(DSP) of the switch may be connected to a separate WAKE# line, allowing
each endpoint to signal WAKE# independently. From figure 5.4 in sec
5.3.3.2, WAKE# can also be terminated at the switch itself. Such topologies
are typically not described in Device Tree, therefore it is out of scope
for this series.

To support this, the WAKE# should be described in the device tree node of
the endpoint/bridge. If all endpoints share a single WAKE# line, then each
endpoint node shall describe the same WAKE# signal or a single WAKE# in the
Root Port node.

In pci_device_add(), PCI framework will search for the WAKE# in device
node. Once found, register for the wake IRQ through
dev_pm_set_dedicated_wake_irq() associates a wakeup IRQ with a device and
requests it, but the PM core keeps the IRQ disabled by default. The IRQ is
enabled by the PM core, only when the device is permitted to wake the
system, i.e. during system suspend and after runtime suspend, and only when
device wakeup is enabled.

If the same WAKE# GPIO is described in multiple device tree nodes, only the
first device that successfully registers the wake IRQ will succeed, while
subsequent registrations may fail. This limitation does not affect
functional correctness, since WAKE# is only used to bring the link to D0,
and endpoint-specific wakeup handling is resolved later through PME
detection (PME_EN is set in suspend path by PCI core by default).

When the wake IRQ fires, the wakeirq handler invokes pm_runtime_resume() to
bring the device back to an active power state, such as transitioning from
D3cold to D0. Once the device is active and the link is usable, the
endpoint may generate a PME, which is then handled by the PCI core through
PME polling or the PCIe PME service driver to complete the wakeup of the
endpoint.

WAKE# is added in dts schema and merged based on below links.

Link: https://lore.kernel.org/all/20250515090517.3506772-1-krishna.chundru@oss.qualcomm.com/
Link: https://github.com/devicetree-org/dt-schema/pull/170
Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
Acked-by: Manivannan Sadhasivam <mani@kernel.org>
Link: https://patch.msgid.link/20260707-wakeirq_support-v12-1-b4453f5bcc97@oss.qualcomm.com

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