ACPI: scan: Introduce typedef:s for struct acpi_hotplug_context members

Follow the struct acpi_device_ops approach and introduce typedef:s
for the members. It makes code less verbose and more particular on
what parameters we take or types we use.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>