ACPI: button: Eliminate the driver notify callback

ACPI: button: Eliminate the driver notify callback

Rework the ACPI button driver to install notify handlers or fixed
event handlers for the devices it binds to by itself, reduce the
indentation level in its notify handler routine and drop its
notify callback.

This will allow acpi_device_install_notify_handler() and
acpi_device_remove_notify_handler() to be simplified going forward
and it will allow the driver to use different notify handlers for the
lid and for the power and sleep buttons.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Michal Wilczynski <michal.wilczynski@intel.com>