ACPI / dock: Add .uevent() callback to struct acpi_hotplug_context

In order to avoid the need to register special ACPI dock
operations for SATA devices add a .uevent() callback pointer to
struct acpi_hotplug_context and make dock_hotplug_event() use that
callback if available.  Also rename the existing .event() callback
in struct acpi_hotplug_context to .notify() to avoid possible
confusion in the future.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>