ACPI: PCI: PM: Rework root bus notification setup

ACPI: PCI: PM: Rework root bus notification setup

Since pci_acpi_add_bus_pm_notifier() is only suitable for adding ACPI
PM notifiers to root buses, rename it to pci_acpi_add_root_pm_notifier()
and modify it to take an additional "root" argument, which is then used
for passing a PCI root bridge device pointer to acpi_add_pm_notifier().

That function uses it to populate the "dev" field in the context
structure attached to the ACPI device object that will receive the
ACPI "wake" notifications on behalf of the given PCI root bus.  The
context structure in question is passed to pci_acpi_wake_bus(), so
the latter can be simplified quite a bit now because the target PCI
host bridge structure address can be derived from "dev".

No intentional functional impact.

This change will also facilitate a subsequent update related to the
registration of wakeup sources.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Armin Wolf <W_Armin@gmx.de>
[ rjw: Kerneldoc comment fixup ]
Link: https://patch.msgid.link/2395263.ElGaqSPkdT@rafael.j.wysocki
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>